cue/load: remove impossible condition

Change-Id: Ic9e28d2e1fe493d7ff37adb463d07158982b9f92
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2320
Reviewed-by: Marcel van Lohuizen <mpvl@google.com>
diff --git a/cue/load/read_test.go b/cue/load/read_test.go
index bb5004a..aeb2b1d 100644
--- a/cue/load/read_test.go
+++ b/cue/load/read_test.go
@@ -128,7 +128,7 @@
 			}
 			continue
 		}
-		if err == nil && tt.err != "" {
+		if tt.err != "" {
 			t.Errorf("#%d: success, expected %q", i, tt.err)
 			continue
 		}