[x86] Remove an over-reduced test case. This would need to be
intergrated much more fully into some logical part of the backend to
really understand what it is trying to accomplish and how to update it.
I suspect it no longer holds enough value to be worth having.
[x86] Regenerate precise checks for a couple of test cases and remove
a test case that was just grepping the debug stats output rather than
actually checking the generated code for anything useful.