clean up when finished.

don't set PLAN9
don't set PLAN9

src/cmd/graph/graph.c

@@ -243,11 +243,6 @@ void limread(struct xy *p, int *argcp, char ***argvp){
 	p->xqf = 1;
 }
 
-int
-isdigit(char c){
-	return '0'<=c && c<='9';
-}
-
 int
 numb(float *np, int *argcp, char ***argvp){
 	char c;

src/cmd/graph/mkfile

@@ -1,4 +1,3 @@
-PLAN9=../../..
 <$PLAN9/src/mkhdr
 
 TARG=graph