rename Optional arguments to Utility arguments, since all arguments are optional

although, arguably, they all provide Utility as well.

wait, was this 'Optional arguments' header supposed to introduce *all* of the arguments, and just has a couple misc ones under it, as a sort of pun? Well, whatever.

Author: wyattscarpenter

mypy/main.py

@@ -551,7 +551,7 @@ def add_invertible_flag(
     #     long and will break up into multiple lines if we include that prefix, so for consistency
     #     we omit the prefix on all links.)
 
-    general_group = parser.add_argument_group(title="Optional arguments")
+    general_group = parser.add_argument_group(title="Utility arguments")
     general_group.add_argument(
         "-h", "--help", action="help", help="Show this help message and exit"
     )