sage --fixdoctests: Improve help string

Author: Matthias Koeppe

src/bin/sage-fixdoctests

@@ -67,7 +67,7 @@ parser.add_argument("--full-tracebacks", default=False, action="store_true",
 parser.add_argument("--only-tags", default=False, action="store_true",
                     help="only add '# optional/needs' tags where needed, ignore other failures")
 parser.add_argument("--probe", metavar="FEATURES", type=str, default='',
-                    help="check whether '# optional/needs' tags are still needed, remove these")
+                    help="check whether '# optional/needs' tags are still needed, remove those not needed")
 parser.add_argument("--keep-both", default=False, action="store_true",
                     help="do not replace test results; duplicate the test instead, showing both results, and mark both copies '# optional'")
 parser.add_argument("--overwrite", default=False, action="store_true",