runtime: avoid large object stack copy in traceStackTable.dump

Following up on the previous CL, this CL removes a unnecessary stack
copy of a large object in a range loop. This drops another 64 KiB from
(*traceStackTable).dump's stack frame so it is now roughly 80 bytes
depending on architecture, which will easily fit on the system stack.

For #53979.

Change-Id: I16f642f6f1982d0ed0a62371bf2e19379e5870eb
Reviewed-on: https://go-review.googlesource.com/c/go/+/422955
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Austin Clements <austin@google.com>

Author: aclements

Diff for: src/runtime/trace.go

@@ -1060,8 +1060,8 @@ func traceFrames(bufp traceBufPtr, pcs []uintptr) ([]traceFrame, traceBufPtr) {
 // releases all memory and resets state.
 func (tab *traceStackTable) dump() {
 	bufp := traceFlush(0, 0)
-	for _, stk := range tab.tab {
-		stk := stk.ptr()
+	for i, _ := range tab.tab {
+		stk := tab.tab[i].ptr()
 		for ; stk != nil; stk = stk.link.ptr() {
 			var frames []traceFrame
 			frames, bufp = traceFrames(bufp, stk.stack())