Revert r330492: [clang-tidy] add new check to find out objc ivars which do not have prefix '_'

This commit has been breaking most bots for a day now. There is a fix
proposed in https://reviews.llvm.org/D45912 but when I applied that
I just got different errors. Reverting to get our bots back to green.

llvm-svn: 330528