Revert "AMDGPU: Try to commute sub of boolean ext"

This reverts commit 69fcfb7d.

As shown in the test I attached to this commit, the change I reverted
causes a problem with "zext(cc1) - zext(cc2)". It commuted
the operands to the sub and used different logic to select the addc/subc
instruction:
   sub zext (setcc), x => addcarry 0, x, setcc
   sub sext (setcc), x => subcarry 0, x, setcc

... but that is bogus. I believe it is not possible to fold those commuted
patterns into any form of addcarry or subcarry. It may have worked as
intended before "AMDGPU: Change boolean content type to 0 or 1" because
the setcc was considered to be -1 rather than 1.

Differential Revision: https://reviews.llvm.org/D70978

Change-Id: If2139421aa6c935cbd1d925af58fe4a4aa9e8f43