Remove shift amount flavor. It isn't actually complete enough to

Remove shift amount flavor.  It isn't actually complete enough to
be useful, and it's currently unused.  (Some issues: it isn't actually
rich enough to capture the semantics on many architectures, and
semantics can vary depending on the type being shifted.)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76633 91177308-0d34-0410-b5e6-96231b3b80d8