Rename ArrayRef::keep_front / keep_back to take_front / take_back.

The name decided on was take_, but I only updated it for StringRef
and forgot to do it for ArrayRef.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280126 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed