runtime: remove out-of-date comments about frame skipping

skipPleaseUseCallersFrames was removed in CL 152537.

Change-Id: Ide47feec85a33a6fb6882e16baf9e21492521640
Reviewed-on: https://go-review.googlesource.com/c/go/+/325949
Trust: Matthew Dempsky <[email protected]>
Run-TryBot: Matthew Dempsky <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: mdempsky

src/runtime/traceback.go

@@ -56,18 +56,14 @@ func tracebackdefers(gp *g, callback func(*stkframe, unsafe.Pointer) bool, v uns
 	}
 }
 
-const sizeofSkipFunction = 256
-
 // Generic traceback. Handles runtime stack prints (pcbuf == nil),
 // the runtime.Callers function (pcbuf != nil), as well as the garbage
 // collector (callback != nil).  A little clunky to merge these, but avoids
 // duplicating the code and all its subtlety.
 //
 // The skip argument is only valid with pcbuf != nil and counts the number
 // of logical frames to skip rather than physical frames (with inlining, a
-// PC in pcbuf can represent multiple calls). If a PC is partially skipped
-// and max > 1, pcbuf[1] will be runtime.skipPleaseUseCallersFrames+N where
-// N indicates the number of logical frames to skip in pcbuf[0].
+// PC in pcbuf can represent multiple calls).
 func gentraceback(pc0, sp0, lr0 uintptr, gp *g, skip int, pcbuf *uintptr, max int, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer, flags uint) int {
 	if skip > 0 && callback != nil {
 		throw("gentraceback callback cannot be used with non-zero skip")