[dev.ssa] cmd/compile: don't issue nops for static data

It confuses live variable analysis to have a bunch of unreachable
no-ops at the end of a function.  Symptom is:
    gc/plive.go:483 panic: interface conversion: interface {} is nil, not *gc.BasicBlock

I don't see any reason why the old compiler needs these no-ops either.
all.bash passes with the equivalent code removed on master.

Change-Id: Ifcd2c3e139aa16314f08aebc9079b2fb7aa60556
Reviewed-on: https://go-review.googlesource.com/16132
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/gc/sinit.go

@@ -1431,9 +1431,6 @@ func gen_as_init(n *Node, reportOnly bool) bool {
 	case OSLICEARR:
 		if nr.Right.Op == OKEY && nr.Right.Left == nil && nr.Right.Right == nil {
 			nr = nr.Left
-			if !reportOnly {
-				gused(nil) // in case the data is the dest of a goto
-			}
 			nl := nr
 			if nr == nil || nr.Op != OADDR {
 				goto no