internal/protobuf: record position information

for both errors and in the AST.

Removes the error type, which now implements the
standard CUE error conventions.

Change-Id: I7a4198a9cf9b38622f14f63df827f3f9730fe4b5
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2341
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/internal/protobuf/protobuf_test.go b/internal/protobuf/protobuf_test.go
index e21a126..5049281 100644
--- a/internal/protobuf/protobuf_test.go
+++ b/internal/protobuf/protobuf_test.go
@@ -26,7 +26,7 @@
 	"github.com/kr/pretty"
 )
 
-var update *bool = flag.Bool("update", false, "update the test output")
+var update = flag.Bool("update", false, "update the test output")
 
 func TestParseDefinitions(t *testing.T) {
 	testCases := []string{