[APInt] Remove the And/Or/Xor/Not functions from the APIntOps namespace.

Summary:
They aren't used anywhere in tree and its preferable to use the &, |, ^, or ~ operators.

With my patch to add rvalue reference support to &, |, ^ operators it also becomes less performant to use these functions.

Reviewers: RKSimon, davide, hans

Reviewed By: RKSimon

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30613

llvm-svn: 296990