[CallSite removal] Move the verifier to use `CallBase` instead of the
`CallSite` wrapper.

Mostly mechanical, but I've tried to tidy up code where it made sense to
do so.

Differential Revision: https://reviews.llvm.org/D56143

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350507 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed