runtime: remove # from gctrace line

Whenever someone pastes gctrace output into GitHub, it helpfully turns
the GC cycle number into a link to some unrelated issue. Prevent this
by removing the pound before the cycle number. The fact that this is a
cycle number is probably more obvious at a glance than most of the
other numbers.

Change-Id: Ifa5fc7fe6c715eac50e639f25bc36c81a132ffea
Reviewed-on: https://go-review.googlesource.com/12413Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/mgc.go

@@ -1136,7 +1136,7 @@ func gc(mode int) {
 
 		var sbuf [24]byte
 		printlock()
-		print("gc #", memstats.numgc,
+		print("gc ", memstats.numgc,
 			" @", string(itoaDiv(sbuf[:], uint64(tSweepTerm-runtimeInitTime)/1e6, 3)), "s ",
 			util, "%: ")
 		prev := tSweepTerm