During development some tracing routines were added that are not
needed in the release. These included GCstarttimes, GCendtimes, and
GCprinttimes.
Fixes #10462

Change-Id: I0788e6409d61038571a5ae0cbbab793102df0a65
Reviewed-on: https://go-review.googlesource.com/9689Reviewed-by: Austin Clements <austin@google.com>