cmd/compile/internal/gc: remove dead code found by vet

See report in commit 3c9fa388.

Change-Id: I74a5995a1c1ca62b8d01857e89b084502e7da928
Reviewed-on: https://go-review.googlesource.com/14170Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1220,7 +1220,6 @@ func visitComponents(t *Type, startOffset int64, f func(elem *Type, elemOffset i
 	case TINTER:
 		return f(itable, startOffset) &&
 			f(Ptrto(Types[TUINT8]), startOffset+int64(Widthptr))
-		return true
 
 	case TSTRING:
 		return f(Ptrto(Types[TUINT8]), startOffset) &&