Deprecate unused LassoSelector event handlers.

These are unused since 61ab6df (and have trivial replacements if
someone *really* wants to call them manually, which seems unlikely).

Author: anntzer

doc/api/next_api_changes/deprecations/20603-AL.rst

@@ -0,0 +1,3 @@
+``LassoSelector.onpress`` and ``LassoSelector.onrelease``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+... are deprecated (they are straight aliases for ``press`` and ``release``).

lib/matplotlib/widgets.py

@@ -3061,13 +3061,15 @@ def __init__(self, ax, onselect=None, useblit=True, lineprops=None,
         self.ax.add_line(self.line)
         self.artists = [self.line]
 
+    @_api.deprecated("3.5", alternative="press")
     def onpress(self, event):
         self.press(event)
 
     def _press(self, event):
         self.verts = [self._get_data(event)]
         self.line.set_visible(True)
 
+    @_api.deprecated("3.5", alternative="release")
     def onrelease(self, event):
         self.release(event)
 
@@ -3083,9 +3085,7 @@ def _onmove(self, event):
         if self.verts is None:
             return
         self.verts.append(self._get_data(event))
-
         self.line.set_data(list(zip(*self.verts)))
-
         self.update()