runtime: Remove unused runtime.write from linux/amd64

Also minor reformatting.

R=rsc
CC=golang-dev
https://golang.org/cl/845041

src/pkg/runtime/linux/amd64/sys.s

@@ -10,7 +10,7 @@
 
 TEXT	exit(SB),7,$0-8
 	MOVL	8(SP), DI
-	MOVL	$231, AX	// exitgroup - force all os threads to exi
+	MOVL	$231, AX	// exitgroup - force all os threads to exit
 	SYSCALL
 	RET
 
@@ -36,14 +36,6 @@ TEXT	write(SB),7,$0-24
 	SYSCALL
 	RET
 
-TEXT	·write(SB),7,$0-24
-	MOVL	8(SP), DI
-	MOVQ	16(SP), SI
-	MOVL	24(SP), DX
-	MOVL	$1, AX			// syscall entry
-	SYSCALL
-	RET
-
 TEXT	gettime(SB), 7, $32
 	LEAQ	8(SP), DI
 	MOVQ	$0, SI
@@ -174,7 +166,7 @@ TEXT clone(SB),7,$0
 	// Call fn
 	CALL	R12
 
-	// It shouldn't return.  If it does, exi
+	// It shouldn't return.  If it does, exit
 	MOVL	$111, DI
 	MOVL	$60, AX
 	SYSCALL