Remove unused MTMSRD_L macro and re-add accidentally deleted comment.
In the commit that added PowerPC Pair Singles, Ben accidentally removed
a comment and re-added an unused MTMSRD_L macro Alan had recently deleted.
This was probably just an oversite when he was refreshing his patch to
trunk.
opcodes/
* ppc-opc.c: Add comment accidentally removed by old commit.
(MTMSRD_L): Delete.