reflect/protoreflect: remove bool output for Descriptor.Parent method

This is a breaking change.

The equivalent replacement logic is to trivially check whether the
parent descriptor is not nil.

Change-Id: I5c89c1d9f29f9e6f721bbfbcf7774188d8f0086a
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/175987
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/legacy_file_test.go b/internal/impl/legacy_file_test.go
index d4c5890..dad814f 100644
--- a/internal/impl/legacy_file_test.go
+++ b/internal/impl/legacy_file_test.go
@@ -421,8 +421,8 @@
 				name := v.Type().Method(i).Name
 				if m := v.Method(i); m.Type().NumIn() == 0 && m.Type().NumOut() == 1 {
 					switch name {
-					case "ParentFile":
-						// Ignore parent file to avoid recursive cycle.
+					case "ParentFile", "Parent":
+						// Ignore parents to avoid recursive cycle.
 					case "Index":
 						// Ignore index since legacy descriptors have no parent.
 					case "Options":