Formatter: Remove now-unneeded code for formatting ':'s in ObjC method decls.

The more general code for formatting ObjC method exprs does this and more,
it's no longer necessary to special-case this. No behavior change.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174843 91177308-0d34-0410-b5e6-96231b3b80d8