tcg/s390x: Remove DISTINCT_OPERANDS facility check

The distinct-operands facility is bundled into facility 45,
along with load-on-condition.  We are checking this at startup.
Remove the a0 == a1 checks for 64-bit sub, and, or, xor, as there
is no space savings for avoiding the distinct-operands insn.

Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>