We don't need the JSStrictNotEqual operator in the compiler, because
this is never generated by the BytecodeGraphBuilder, and the code in
the AstGraphBuilder was dead code. Also remove the backing builtin
StrictNotEqual.

R=mstarzinger@chromium.org
BUG=v8:5267

Review-Url: https://codereview.chromium.org/2727003006
Cr-Commit-Position: refs/heads/master@{#43594}