runtime: remove unused declarations from mgc0.c.

R=rsc
CC=golang-dev
https://golang.org/cl/4252063

src/pkg/runtime/mgc0.c

@@ -53,7 +53,6 @@ enum {
 static uint64 nlookup;
 static uint64 nsizelookup;
 static uint64 naddrlookup;
-static uint64 nhandoff;
 static int32 gctrace;
 
 typedef struct Workbuf Workbuf;
@@ -71,10 +70,8 @@ extern byte end[];
 static G *fing;
 static Finalizer *finq;
 static int32 fingwait;
-static uint32 nfullwait;
 
 static void runfinq(void);
-static bool bitlookup(void*, uintptr**, uintptr*, int32*);
 static Workbuf* getempty(Workbuf*);
 static Workbuf* getfull(Workbuf*);