Issue #12243: Remove redundant availability notes from getpass docs

Patch by Bryce Verdier.

Doc/library/getpass.rst

@@ -23,8 +23,6 @@ The :mod:`getpass` module provides two functions:
    a warning message to *stream* and reading from ``sys.stdin`` and
    issuing a :exc:`GetPassWarning`.
 
-   Availability: Macintosh, Unix, Windows.
-
    .. note::
       If you call getpass from within IDLE, the input may be done in the
       terminal you launched IDLE from rather than the idle window itself.
@@ -36,7 +34,7 @@ The :mod:`getpass` module provides two functions:
 
 .. function:: getuser()
 
-   Return the "login name" of the user. Availability: Unix, Windows.
+   Return the "login name" of the user.
 
    This function checks the environment variables :envvar:`LOGNAME`,
    :envvar:`USER`, :envvar:`LNAME` and :envvar:`USERNAME`, in order, and returns