argparsing: remove "map_long_option" Action attribute support

This feature was added in commit
007a77c2ba, but was never used in pytest
itself. A GitHub code search doesn't find any users either (only pytest
repo copies). It seems safe to clean up.

src/_pytest/config/argparsing.py

@@ -409,8 +409,6 @@ class DropShorterLongHelpFormatter(argparse.HelpFormatter):
     """shorten help for long options that differ only in extra hyphens
 
     - collapse **long** options that are the same except for extra hyphens
-    - special action attribute map_long_option allows suppressing additional
-      long options
     - shortcut if there are only two options and one of them is a short one
     - cache result on action object as this is called at least 2 times
     """
@@ -434,9 +432,6 @@ class DropShorterLongHelpFormatter(argparse.HelpFormatter):
             action._formatted_action_invocation = orgstr
             return orgstr
         return_list = []
-        option_map = getattr(action, "map_long_option", {})
-        if option_map is None:
-            option_map = {}
         short_long = {}  # type: Dict[str, str]
         for option in options:
             if len(option) == 2 or option[2] == " ":
@@ -446,12 +441,11 @@ class DropShorterLongHelpFormatter(argparse.HelpFormatter):
                     'long optional argument without "--": [%s]' % (option), self
                 )
             xxoption = option[2:]
-            if xxoption.split()[0] not in option_map:
-                shortened = xxoption.replace("-", "")
-                if shortened not in short_long or len(short_long[shortened]) < len(
-                    xxoption
-                ):
-                    short_long[shortened] = xxoption
+            shortened = xxoption.replace("-", "")
+            if shortened not in short_long or len(short_long[shortened]) < len(
+                xxoption
+            ):
+                short_long[shortened] = xxoption
         # now short_long has been filled out to the longest with dashes
         # **and** we keep the right option ordering from add_argument
         for option in options:

testing/test_parseopt.py

@@ -205,11 +205,11 @@ class TestParser:
         )
         parser.add_argument(
             "-t", "--twoword", "--duo", "--two-word", "--two", help="foo"
-        ).map_long_option = {"two": "two-word"}
+        )
         # throws error on --deux only!
         parser.add_argument(
             "-d", "--deuxmots", "--deux-mots", action="store_true", help="foo"
-        ).map_long_option = {"deux": "deux-mots"}
+        )
         parser.add_argument("-s", action="store_true", help="single short")
         parser.add_argument("--abc", "-a", action="store_true", help="bar")
         parser.add_argument("--klm", "-k", "--kl-m", action="store_true", help="bar")
@@ -221,7 +221,7 @@ class TestParser:
         )
         parser.add_argument(
             "-x", "--exit-on-first", "--exitfirst", action="store_true", help="spam"
-        ).map_long_option = {"exitfirst": "exit-on-first"}
+        )
         parser.add_argument("files_and_dirs", nargs="*")
         args = parser.parse_args(["-k", "--duo", "hallo", "--exitfirst"])
         assert args.twoword == "hallo"