Drop UBUNTU_MENUPROXY=0 workaround
wxWidgets 2.6 did not show menus correct on the global menu applet in
Unity in 2010 ([Ubuntu bug #662007](https://launchpad.net/bugs/662077)).
The environment variable `UBUNTU_MENUPROXY` was set as workaround.
Audacity 3.2.0 with wxWidgets 3.2 on Ubuntu 22.10 (kinetic) works fine
under the Unity desktop. Therefore drop the old workaround.
Forwarded: https://github.com/audacity/audacity/pull/3701
Signed-off-by: Benjamin Drung <benjamin.drung@canonical.com>
Gbp-Pq: Name Drop-UBUNTU_MENUPROXY-0-workaround.patch