Move widget.{get,set}_active to AxisWidget.

The method was previously defined only for RectangleSelectors (matplotlib#3375).

Also, an redundant line was removed (RectangleSelectors are already set
active on __init__ by the superclass).

lib/matplotlib/widgets.py

@@ -111,6 +111,16 @@ def disconnect_events(self):
         for c in self.cids:
             self.canvas.mpl_disconnect(c)
 
+    def set_active(self, active):
+        """Set whether the widget is active.
+        """
+        self.active = active
+
+    def get_active(self):
+        """Get whether the widget is active.
+        """
+        return self.active
+
     def ignore(self, event):
         """Return True if event should be ignored.
 
@@ -1393,7 +1403,6 @@ def __init__(self, ax, onselect, drawtype='box',
         self.connect_event('button_release_event', self.release)
         self.connect_event('draw_event', self.update_background)
 
-        self.active = True                    # for activation / deactivation
         self.to_draw = None
         self.background = None
 
@@ -1575,17 +1584,6 @@ def onmove(self, event):
             self.update()
             return False
 
-    def set_active(self, active):
-        """
-        Use this to activate / deactivate the RectangleSelector
-        from your program with an boolean parameter *active*.
-        """
-        self.active = active
-
-    def get_active(self):
-        """ Get status of active mode (boolean variable)"""
-        return self.active
-
 
 class LassoSelector(AxesWidget):
     """Selection curve of an arbitrary shape.