Remove comment in security.rst about MySQL with PHP <= 5.3.6
Remove comment in security.rst about MySQL with PHP <= 5.3.6

kimhemsoe/dbal,mikeSimonson/dbal,AlexDpy/dbal,lcobucci/dbal,lafourchette/dbal,doctrine/dbal,doctrine/dbal,bspeterson/dbal,deeky666/dbal,DHager/dbal,v-bartusevicius/dbal,BenMorel/dbal,stof/dbal,helicon-os/doctrine-dbal,mRoca/dbal,helicon-os/doctrine-dbal,bspeterson/dbal,BenMorel/dbal,Tobion/dbal,AlexDpy/dbal,deeky666/dbal,gencer/dbal,vortgo/dbal,kimhemsoe/dbal,vortgo/dbal,drieschel/dbal,DHager/dbal,stchr/dbal,gencer/dbal,drieschel/dbal,stchr/dbal,lcobucci/dbal,Tobion/dbal,v-bartusevicius/dbal,stof/dbal,vutung2311/dbal,mRoca/dbal,vutung2311/dbal,mikeSimonson/dbal,lafourchette/dbal