Revert "cmd/compile/internal/gc: steps towards work-queue"

Revert "cmd/compile/internal/gc: steps towards work-queue"

This reverts commit CL 520611.

Reason for revert: #62156.

Change-Id: Iebd17bdfc00824de3d5011a74d071a41c4fa06f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/521155
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>