Revert "cmd/compile/internal/noder: limit the number of goroutine"

This reverts commit c274a7c0.

Reason for revert: this can cause a compiler deadlock, and there's
no demonstrable benefit to making the change.

Change-Id: I42325ddea68d37db16fd0061c5baaee112b755b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/308369


Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>