runtime: remove unused RaceSemacquire declaration

These functions are not defined and are not used.

Fixes #19290

Change-Id: I2978147220af83cf319f7439f076c131870fb9ee
Reviewed-on: https://go-review.googlesource.com/37448Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/race.go

@@ -17,9 +17,6 @@ func RaceWrite(addr unsafe.Pointer)
 func RaceReadRange(addr unsafe.Pointer, len int)
 func RaceWriteRange(addr unsafe.Pointer, len int)
 
-func RaceSemacquire(s *uint32)
-func RaceSemrelease(s *uint32)
-
 func RaceErrors() int {
 	var n uint64
 	racecall(&__tsan_report_count, uintptr(unsafe.Pointer(&n)), 0, 0, 0)