Merge pull request matplotlib#25708 from anntzer/uqm

Deprecate unused NavigationToolbar2QT signal.

Author: QuLogic

doc/api/next_api_changes/deprecations/25708-AL.rst

@@ -0,0 +1,3 @@
+``NavigationToolbar2QT.message`` is deprecated
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+... with no replacement.

lib/matplotlib/backends/backend_qt.py

@@ -622,7 +622,8 @@ def set_window_title(self, title):
 
 
 class NavigationToolbar2QT(NavigationToolbar2, QtWidgets.QToolBar):
-    message = QtCore.Signal(str)
+    _message = QtCore.Signal(str)  # Remove once deprecation below elapses.
+    message = _api.deprecate_privatize_attribute("3.8")
 
     toolitems = [*NavigationToolbar2.toolitems]
     toolitems.insert(
@@ -741,7 +742,7 @@ def zoom(self, *args):
         self._update_buttons_checked()
 
     def set_message(self, s):
-        self.message.emit(s)
+        self._message.emit(s)
         if self.coordinates:
             self.locLabel.setText(s)