[FileCheck] Remove FileCheck prefix in API
Summary:
When FileCheck was made a library, types in the public API were renamed
to add a FileCheck prefix, such as Pattern to FileCheckPattern. Many
types were moved into a private interface and thus don't need this
prefix anymore. This commit removes those unneeded prefixes.
Reviewers: jhenderson, jdenny, probinson, grimar, arichardson, rnk
Reviewed By: jhenderson
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72186