config: remove Parser._ininames

Doesn't seem needed. Maybe it was useful before dicts had guaranteed
iteration order? `pytest --help` output is unchanged.

Author: bluetech

src/_pytest/config/argparsing.py

@@ -51,7 +51,6 @@ def __init__(
         self._processopt = processopt
         self._usage = usage
         self._inidict: dict[str, tuple[str, str, Any]] = {}
-        self._ininames: list[str] = []
         # Maps alias -> canonical name.
         self._ini_aliases: dict[str, str] = {}
         self.extra_info: dict[str, Any] = {}
@@ -244,7 +243,6 @@ def addini(
             default = get_ini_default_for_type(type)
 
         self._inidict[name] = (help, type, default)
-        self._ininames.append(name)
 
         for alias in aliases:
             if alias in self._inidict:

src/_pytest/helpconfig.py

@@ -184,7 +184,7 @@ def showhelp(config: Config) -> None:
     columns = tw.fullwidth  # costly call
     indent_len = 24  # based on argparse's max_help_position=24
     indent = " " * indent_len
-    for name in config._parser._ininames:
+    for name in config._parser._inidict:
         help, type, _default = config._parser._inidict[name]
         if help is None:
             raise TypeError(f"help argument cannot be None for {name}")