minor #739 Remove unused twig-extensions dependency (tommygnr)
minor #739 Remove unused twig-extensions dependency (tommygnr)

This PR was submitted for the 2.3 branch but it was merged into the 2.7 branch instead (closes #739).

Discussion
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Remove unused twig-extensions dependency

The ```twig/extensions``` library is not actually used or enabled in the symfony standard distribution so its inclusion in the composer.json file seems unnecessary. I did quite a bit of digging around to work out why it was ever included and as best I can tell it was because in the betas of ```2.0``` there was a convenient way to register these extensions in the twig configuration block. That approach was abandoned in https://github.com/symfony/symfony/commit/96045739b198b030ab159425ce19614fe2e0e665

Commits
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1272c9f Remove unused twig-extensions dependency

RuntyCybin/symfony-standard,dkarvounaris/symfony-standard,symfony/symfony-standard,ctrl-f5/symfony-standard,proteichik/testApp,fabpot/symfony-standard,kmelia/fresh-symfony,zanderbaldwin/symfony-layers,Tobion/symfony-standard,papaavola/symfony-standard,vincentaubert/symfony-standard,pjcdawkins/tmp-symfony-demo,javiereguiluz/symfony-standard,unewochialat/symfony-standard,Cartesia/01,sulu-io/sulu-standard,yelmontaser/symfony-standard,twisted-socket/stage-plots,rajkamalganeshvivid/symfony-standard,apnet/symfony-standard-edition,Soullivaneuh/symfony-standard,kmelia/fresh-symfony,WolfMicrosystems/symfony-wms,fahadonline/sulu,zanderbaldwin/symfony-layers,fahadonline/sulu,formapro-forks/api-basic,SymfonyId/Skeleton,SymfonyId/Skeleton,xiaobudongzhang/symfony-standard,liip-forks/symfony-standard,yhoiseth/notelite.net,tristanbes/symfony-standard,Cartesia/01,ucay/Skeleton,Clastic/StandardEdition,orodsem/trout,Cartesia/01,simonjcarr/symfony_rest,jakzal/symfony-standard,fabpot/symfony-standard,wachterjohannes/sulu-standard,Soullivaneuh/symfony-standard,ovelasquez/ussi,havvg/symfony-propel-edition,propelorm/symfony-propel-edition,aerrasti/iemedebe,umpirsky/symfony-standard,dunglas/symfony-standard,phospr/symfony-starter,apnet/symfony-standard-edition,lyrixx/symfony-standard,bamarni/symfony-docker,stof/symfony-standard,fduch/symfony-standard-workflow,debruyne0/symfony,trsteel88/symfony-standard,jbdelhommeau/symfony-standard,vincentaubert/symfony-standard,debruyne0/symfony,formapro-forks/api-basic,GulDmitry/music-diff,taylankasap/symfony-standard,yelmontaser/symfony-standard,ucay/Skeleton,mweimerskirch/symfony-standard,GulDmitry/music-diff,dkarvounaris/symfony-standard,jbdelhommeau/symfony-standard,b00giZm/symfony-boilerplate-app,symfony-cmf/standard-edition,uttam-vi/pardawala,symfony-cmf/standard-edition,shamcode/symfony-testing,gencer/symfony-standard,Rvanlaak/symfony-standard,orodsem/trout,dunglas/symfony-standard,ewgRa/symfony-standard,ovelasquez/ussi,wachterjohannes/sulu-standard,havvg/symfony-standard-propel,rajkamalganeshvivid/symfony-standard,xiaobudongzhang/symfony-standard,sulu-io/sulu-standard,proteichik/testApp,kmelia/fresh-symfony,the-software-factory/superhero-api,yhoiseth/notelite.net,glavweb/symfony-standard,black-project/black-standard,Baachi/symfony-standard,simonjcarr/symfony_rest,liip-forks/symfony-standard,tristanbes/symfony-standard,twisted-socket/stage-plots,trsteel88/symfony-standard,fahadonline/sulu,jakzal/symfony-standard,symfony/symfony-standard,mweimerskirch/symfony-standard,platformsh/platformsh-example-symfony,vincentchalamon/phpunit-bridge,Clastic/StandardEdition,theodo/theodo-kata,shadowtje1990/symfony_todo_api,aerrasti/iemedebe,AlexeyKupershtokh/symfony-standard,lyrixx/symfony-standard,WolfMicrosystems/symfony-wms,havvg/symfony-standard-propel,egeloen/symfony-standard,black-project/black-standard,fahadonline/sulu,pjcdawkins/tmp-symfony-demo,AlexeyKupershtokh/symfony-standard,ucay/Skeleton,theodo/theodo-kata,fduch/symfony-standard-workflow,GulDmitry/music-diff,bocharsky-bw/symfony-standard,RuntyCybin/symfony-standard,havvg/symfony-propel-edition,stof/symfony-standard,b00giZm/symfony-boilerplate-app,Spea/symfony-standard,wachterjohannes/sulu-standard,Spea/symfony-standard,bocharsky-bw/symfony-standard,umpirsky/symfony-standard,Clastic/StandardEdition,shamcode/symfony-testing,uttam-vi/pardawala,egeloen/symfony-standard,Tobion/symfony-standard,UxorialRook/symfony-standard,gencer/symfony-standard,b00giZm/symfony-boilerplate-app,the-software-factory/superhero-api,orodsem/trout,ewgRa/symfony-standard,uttam-vi/pardawala,unewochialat/symfony-standard,ctrl-f5/symfony-standard,shadowtje1990/symfony_todo_api,bamarni/symfony-docker,Baachi/symfony-standard,glavweb/symfony-standard,GulDmitry/music-diff,papaavola/symfony-standard,platformsh/platformsh-example-symfony,vincentchalamon/phpunit-bridge,phospr/symfony-starter,javiereguiluz/symfony-standard,ovelasquez/ussi,apnet/symfony-standard-edition,sulu-io/sulu-standard,taylankasap/symfony-standard,propelorm/symfony-propel-edition,UxorialRook/symfony-standard