Removed the 'id' AST matcher, which is superseded by '.bind()'

Summary:
The 'id' matcher is not even included in the AST Matchers Reference
document, so I don't expect there to be a significant number of users.

There's no reason to provide two ways to do the exact same thing that
only have a minor syntactic difference.

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66462

llvm-svn: 369380