runtime: fix double symbol definition

runfinqv is already defined the same way on line 271.
There may also be something to fix in compiler/linker wrt diagnostics.
Fixes #7375.

LGTM=bradfitz
R=golang-codereviews, dave, bradfitz
CC=golang-codereviews
https://golang.org/cl/67850044

src/pkg/runtime/mgc0.c

@@ -2182,8 +2182,6 @@ readgogc(void)
 	return runtime·atoi(p);
 }
 
-static FuncVal runfinqv = {runfinq};
-
 void
 runtime·gc(int32 force)
 {