runtime: cleanup comments from asm_ppc64x.s improvements
CL 706395 consolidated the aix and elf startup code, further
update the comments to reflect this.
Change-Id: Iccb98008b3fe4a4b08e55ee822924fad76846cc2
Reviewed-on: https://go-review.googlesource.com/c/go/+/708355
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Paul Murphy <paumurph@redhat.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Keith Randall <khr@google.com>