target/sparc: Remove CC_OP_SUB, CC_OP_SUBX, CC_OP_TSUB

These are all related and implementable with common code.

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>