Remove update_checker

Doesn't work on Python3 and would probably annoy more people than it helps if it was working.

Traceback (most recent call last):
  File "/home/pbarker/.local/lib/python3.10/site-packages/dronecan_gui_tool/update_checker.py", line 157, in do_background_check
    update_reference = _do_pip_check()
  File "/home/pbarker/.local/lib/python3.10/site-packages/dronecan_gui_tool/update_checker.py", line 84, in _do_pip_check
    data = json.loads(data.decode('utf8'), encoding='utf8')
  File "/usr/lib/python3.10/json/__init__.py", line 359, in loads
    return cls(**kw).decode(s)
TypeError: JSONDecoder.__init__() got an unexpected keyword argument 'encoding'
2024-01-12 11:27:37,946 INFO dronecan_gui_tool.update_checker Update checker stopped

dronecan_gui_tool/main.py

@@ -69,7 +69,6 @@
 from .version import __version__
 from .setup_window import run_setup_window
 from .active_data_type_detector import ActiveDataTypeDetector
-from . import update_checker
 
 from .widgets import show_error, get_icon, get_app_icon
 from .widgets.node_monitor import NodeMonitorWidget
@@ -635,11 +634,6 @@ def main():
     window = MainWindow(node, iface, iface_kwargs)
     window.show()
 
-    try:
-        update_checker.begin_async_check(window)
-    except Exception:
-        logger.error('Could not start update checker', exc_info=True)
-
     logger.info('Init complete, invoking the Qt event loop')
     exit_code = app.exec_()