Why I can't remove iTunes and how to remove it?
If you just want to prevent it from launching, running

sudo chmod 000 /Applications/iTunes.app


should do the trick. Needs to be repeated after every OS X/iTunes update, but this also applies for any solutions involving removal of standard applications.

PS: Just to put things into perspective as far as disk space is concerned:

root@Mithos:/Applications$ du -sm iTunes.app Chess.app Game\ Center.app Stickies.app Photo\ Booth.app Photos.app 
191 iTunes.app
5   Chess.app
3   Game Center.app
5   Stickies.app
5   Photo Booth.app
31  Photos.app


Even on a system with just a 128 GB SSD, squeezing out 200 MB doesn't give you much.