runtime: remove outdated comment and related indentation

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/39810043

src/pkg/runtime/mgc0.c

@@ -409,11 +409,6 @@ flushptrbuf(Scanbuf *sbuf)
 			runtime·throw("ptrbuf has to be smaller than WorkBuf");
 	}
 
-	// TODO(atom): This block is a branch of an if-then-else statement.
-	//             The single-threaded branch may be added in a next CL.
-	{
-		// Multi-threaded version.
-
 	while(ptrbuf < ptrbuf_end) {
 		obj = ptrbuf->p;
 		ti = ptrbuf->ti;
@@ -534,7 +529,6 @@ flushptrbuf(Scanbuf *sbuf)
 		nobj = wbuf->nobj;
 		wp = wbuf->obj + nobj;
 	}
-	}
 
 	sbuf->wp = wp;
 	sbuf->wbuf = wbuf;