cmd/6g: remove unused stosptr variable

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/78030043

src/cmd/6g/galign.c

@@ -22,7 +22,6 @@ vlong MAXWIDTH = 1LL<<50;
 int	addptr = AADDQ;
 int	movptr = AMOVQ;
 int	leaptr = ALEAQ;
-int	stosptr = ASTOSQ;
 int	cmpptr = ACMPQ;
 
 /*
@@ -49,7 +48,6 @@ betypeinit(void)
 		addptr = AADDL;
 		movptr = AMOVL;
 		leaptr = ALEAL;
-		stosptr = ASTOSL;
 		cmpptr = ACMPL;
 		typedefs[0].sameas = TINT32;
 		typedefs[1].sameas = TUINT32;

src/cmd/6g/gg.h

@@ -28,7 +28,6 @@ extern	int	addptr;
 extern	int	cmpptr;
 extern	int	movptr;
 extern	int	leaptr;
-extern	int	stosptr;
 
 /*
  * ggen.c