cmd/compile: remove ir.OGETCALLERPC

cmd/compile: remove ir.OGETCALLERPC

Nothing ever creates this op, so it can be safely removed. Note that SSA
still intrinsifies runtime.getcallerpc.

The similar ir.OGETCALLERSP is still used for defer handling in
typecheck/func.go:tcRecover.

For #54766.

Change-Id: I6bdb2072af2c068080ae977c0cbd4684d0c7c752
Reviewed-on: https://go-review.googlesource.com/c/go/+/613496
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>