[SCEVExpander] Fix comments for functions. NFC.

Bring function documentation for ScalarEvolutionExpander up to code by
not repeating the function name in the comment documenting
functionality.  Reflow the edited comments where needed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234847 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed