When gcWork was first introduced, the compiler's escape analysis
wasn't good enough to detect that that method receiver didn't escape,
so we had to hack around this.

Now that the compiler can figure out this for itself, remove these
hacks.

Change-Id: I9f73fab721e272410b8b6905b564e7abc03c0dfe
Reviewed-on: https://go-review.googlesource.com/19634Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>