cmd/internal/obj/x86: cleanup

Remove duplicate vars, commented out code  and duplicate lines.
When choosing between 2 aliases, on with more uses was chosen.

Change-Id: I7bc15f1693de3f6d378cef9c09469970a659db40
Reviewed-on: https://go-review.googlesource.com/29152
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>