go/internal/gccgoimporter: remove guard on some assertions

Remove unnecessary conditional guard for a couple of assertions in the
type parser's update() method (inspired by comment from Robert). No
change in functionality.

Change-Id: I706a54569e75c6960768247889b7dec3f267dde9
Reviewed-on: https://go-review.googlesource.com/c/go/+/194565
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/internal/gccgoimporter/parser.go

@@ -475,14 +475,12 @@ func (p *parser) reserve(n int) {
 // used to resolve pointers to named types in case they are referenced
 // by embedded fields.
 func (p *parser) update(t types.Type, nlist []interface{}) {
-	if len(nlist) != 0 {
 	if t == reserved {
 		p.errorf("internal error: update(%v) invoked on reserved", nlist)
 	}
 	if t == nil {
 		p.errorf("internal error: update(%v) invoked on nil", nlist)
 	}
-	}
 	for _, n := range nlist {
 		switch n := n.(type) {
 		case int: