GlobalISel: simplify G_ICMP legalization regime.

It's unclear how the old

    %res(32) = G_ICMP { s32, s32 } intpred(eq), %0, %1

is actually different from an s1 verison

    %res(1) = G_ICMP { s1, s32 } intpred(eq), %0, %1

so we'll remove it for now.

llvm-svn: 279843