Revert "gh-140482: Preserve and restore stty echo as a test environment (#140519)"

Reverts #140519
This reverts commit b3c713a.

Reason: The PR leads to spurious "ENV CHANGED" failures when running
tests in an interactive terminal.

Author: colesbury

Lib/test/libregrtest/save_env.py

@@ -9,13 +9,6 @@
 
 from .utils import print_warning
 
-# Import termios to save and restore terminal echo.  This is only available on
-# Unix, and it's fine if the module can't be found.
-try:
-    import termios                                # noqa: F401
-except ModuleNotFoundError:
-    pass
-
 
 class SkipTestEnvironment(Exception):
     pass
@@ -72,7 +65,6 @@ def __init__(self, test_name, verbose, quiet, *, pgo):
                  'shutil_archive_formats', 'shutil_unpack_formats',
                  'asyncio.events._event_loop_policy',
                  'urllib.requests._url_tempfiles', 'urllib.requests._opener',
-                 'stty_echo',
                 )
 
     def get_module(self, name):
@@ -300,24 +292,6 @@ def restore_warnings_showwarning(self, fxn):
         warnings = self.get_module('warnings')
         warnings.showwarning = fxn
 
-    def get_stty_echo(self):
-        termios = self.try_get_module('termios')
-        if not os.isatty(fd := sys.__stdin__.fileno()):
-            return None
-        attrs = termios.tcgetattr(fd)
-        lflags = attrs[3]
-        return bool(lflags & termios.ECHO)
-    def restore_stty_echo(self, echo):
-        termios = self.get_module('termios')
-        attrs = termios.tcgetattr(fd := sys.__stdin__.fileno())
-        if echo:
-            # Turn echo on.
-            attrs[3] |= termios.ECHO
-        else:
-            # Turn echo off.
-            attrs[3] &= ~termios.ECHO
-        termios.tcsetattr(fd, termios.TCSADRAIN, attrs)
-
     def resource_info(self):
         for name in self.resources:
             method_suffix = name.replace('.', '_')