[InstCombine] Fix !prof metadata preservation for invokes

Summary:
Bug noticed by inspection.

Extend the test to handle invokes as well as calls, and rewrite it to
not depend on the inliner and other passes.

Also simplify the call site replacement code with CallSite, similar to
what I did to dead arg elimination and arg promotion (rL300235 and
rL300229).

Reviewers: danielcdh, davidxl

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32041

llvm-svn: 300251