cmd/8l, cmd/6l: avoid zeroing zeroed fields

mal() returns zeroed memory, so zeroing these fields is redundant.

R=golang-dev, bradfitz, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/7096049

src/cmd/6l/obj.c

@@ -485,8 +485,6 @@ loop:
 	p->line = Bget4(f);
 	p->back = 2;
 	p->mode = mode;
-	p->ft = 0;
-	p->tt = 0;
 	zaddr(pn, f, &p->from, h);
 	fromgotype = adrgotype;
 	zaddr(pn, f, &p->to, h);

src/cmd/8l/obj.c

@@ -504,8 +504,6 @@ loop:
 	p->as = o;
 	p->line = Bget4(f);
 	p->back = 2;
-	p->ft = 0;
-	p->tt = 0;
 	zaddr(pn, f, &p->from, h);
 	fromgotype = adrgotype;
 	zaddr(pn, f, &p->to, h);