remove Travis build file (.travis.yml) (#8128)
remove Travis build file (.travis.yml) (#8128)

Motivation:

the Netty project does not use Travis CI.

Modification:

Remove .travis.yml

Result:

No more Travis.
andsel/netty,mikkokar/netty,artgon/netty,fengjiachun/netty,Spikhalskiy/netty,johnou/netty,netty/netty,ejona86/netty,Squarespace/netty,fengjiachun/netty,NiteshKant/netty,gerdriesselmann/netty,netty/netty,jchambers/netty,fenik17/netty,Squarespace/netty,johnou/netty,NiteshKant/netty,bryce-anderson/netty,andsel/netty,bryce-anderson/netty,jchambers/netty,mikkokar/netty,fenik17/netty,artgon/netty,johnou/netty,netty/netty,Spikhalskiy/netty,NiteshKant/netty,tbrooks8/netty,jchambers/netty,andsel/netty,doom369/netty,ejona86/netty,Squarespace/netty,bryce-anderson/netty,doom369/netty,NiteshKant/netty,artgon/netty,ejona86/netty,andsel/netty,fenik17/netty,NiteshKant/netty,fengjiachun/netty,netty/netty,mikkokar/netty,tbrooks8/netty,zer0se7en/netty,zer0se7en/netty,Spikhalskiy/netty,gerdriesselmann/netty,zer0se7en/netty,johnou/netty,doom369/netty,tbrooks8/netty,ejona86/netty,Spikhalskiy/netty,fengjiachun/netty,Spikhalskiy/netty,zer0se7en/netty,tbrooks8/netty,Squarespace/netty,mikkokar/netty,fenik17/netty,doom369/netty,andsel/netty,jchambers/netty,gerdriesselmann/netty,jchambers/netty,johnou/netty,netty/netty,fenik17/netty,zer0se7en/netty,fengjiachun/netty,tbrooks8/netty,Squarespace/netty,doom369/netty,bryce-anderson/netty,ejona86/netty,artgon/netty,gerdriesselmann/netty,bryce-anderson/netty,mikkokar/netty,artgon/netty,gerdriesselmann/netty