Remove redundant no_color() context manager

The functionality is already provided by force_color(False) and
force_not_colorized() which were added since this branch started.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: gpshead

Lib/test/support/__init__.py

@@ -2939,21 +2939,6 @@ def new_setUpClass(cls):
     return cls
 
 
-@contextlib.contextmanager
-def no_color():
-    """Force the terminal to not be colorized."""
-    import _colorize
-    from .os_helper import EnvironmentVarGuard
-
-    with (
-        swap_attr(_colorize, "can_colorize", lambda file=None: False),
-        EnvironmentVarGuard() as env,
-    ):
-        env.unset("FORCE_COLOR", "NO_COLOR", "PYTHON_COLORS")
-        env.set("NO_COLOR", "1")
-        yield
-
-
 @contextlib.contextmanager
 def force_color(color: bool):
     import _colorize