runtime: remove unused moreframesize_minalloc field

It was used to request large stack segment for GC
when it was running not on g0.
Now GC is running on g0 with large stack,
and it is not needed anymore.

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/10242045

src/pkg/runtime/runtime.h

@@ -326,7 +326,6 @@ struct	M
 	void*	racepc;
 	void	(*waitunlockf)(Lock*);
 	void*	waitlock;
-	uint32	moreframesize_minalloc;
 
 	uintptr	settype_buf[1024];
 	uintptr	settype_bufsize;

src/pkg/runtime/stack.c

@@ -173,7 +173,7 @@ runtime·oldstack(void)
 void
 runtime·newstack(void)
 {
-	int32 framesize, minalloc, argsize;
+	int32 framesize, argsize;
 	Stktop *top;
 	byte *stk;
 	uintptr sp;
@@ -196,19 +196,11 @@ runtime·newstack(void)
 		runtime·throw("runtime: stack split argsize");
 	}
 
-	minalloc = 0;
 	reflectcall = framesize==1;
-	if(reflectcall) {
+	if(reflectcall)
 		framesize = 0;
-		// moreframesize_minalloc is only set in runtime·gc(),
-		// that calls newstack via reflect·call().
-		minalloc = m->moreframesize_minalloc;
-		m->moreframesize_minalloc = 0;
-		if(framesize < minalloc)
-			framesize = minalloc;
-	}
 
-	if(reflectcall && minalloc == 0 && m->morebuf.sp - sizeof(Stktop) - argsize - 32 > gp->stackguard) {
+	if(reflectcall && m->morebuf.sp - sizeof(Stktop) - argsize - 32 > gp->stackguard) {
 		// special case: called from reflect.call (framesize==1)
 		// to call code with an arbitrary argument size,
 		// and we have enough space on the current stack.