runtime: remove unnecessary variable decls in asm.s

runtime/asm.s contains two variable declarations that don't seem
needed. The variables are defined in Go and not referenced in
assembly. They were added in 2014 during the C to Go transition.
Maybe they were useful at that time, but not now. Remove them.

Change-Id: Id00d724813d18db47126c2f2b8cacfc9d77ffd4b
Reviewed-on: https://go-review.googlesource.com/c/go/+/192378
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/runtime/asm.s

@@ -12,9 +12,6 @@ DATA runtime·no_pointers_stackmap+0x00(SB)/4, $2
 DATA runtime·no_pointers_stackmap+0x04(SB)/4, $0
 GLOBL runtime·no_pointers_stackmap(SB),RODATA, $8
 
-GLOBL runtime·mheap_(SB), NOPTR, $0
-GLOBL runtime·memstats(SB), NOPTR, $0
-
 // NaCl requires that these skips be verifiable machine code.
 #ifdef GOARCH_amd64
 #define SKIP4 BYTE $0x90; BYTE $0x90; BYTE $0x90; BYTE $0x90