cmd/internal/obj/ppc64: rename and remove aliased optab classifiers

cmd/internal/obj/ppc64: rename and remove aliased optab classifiers

Rename C_LCON, C_SCON, C_ADDCON, C_ANDCON into their aliased names
and remove them.

Change-Id: I8f67cc973f8059e65b81669d91a44500fc136b0a
Reviewed-on: https://go-review.googlesource.com/c/go/+/563097
Run-TryBot: Paul Murphy <murp@ibm.com>
Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>