gst1: Remove deprecated GObject.threads_init()

Ref https://wiki.gnome.org/Projects/PyGObject/Threading

"The requirement to call GObject.threads_init() has been removed from
PyGObject 3.10.2 when using Python native threads with GI (via the
threading module) as well as with GI repositories which manage their own
threads that may call back into Python (like GStreamer callbacks). The
GObject.threads_init() function will still exist for the entire 3.x
series for compatibility reasons but emits a deprecation warning."

mopidy/__main__.py

@@ -9,21 +9,20 @@ import textwrap
 try:
     import gi
     gi.require_version('Gst', '1.0')
-    from gi.repository import GObject, Gst
+    from gi.repository import Gst
 except ImportError:
     print(textwrap.dedent("""
-        ERROR: The GObject and Gst Python packages were not found.
+        ERROR: The GStreamer Python package was not found.
 
-        Mopidy requires GStreamer and GObject to work. These are C libraries
-        with a number of dependencies themselves, and cannot be installed with
-        the regular Python tools like pip.
+        Mopidy requires GStreamer to work. GStreamer is a C library with a
+        number of dependencies itself, and cannot be installed with the regular
+        Python tools like pip.
 
         Please see http://docs.mopidy.com/en/latest/installation/ for
         instructions on how to install the required dependencies.
     """))
     raise
 
-GObject.threads_init()
 Gst.init()
 
 try:

mopidy/audio/scan.py

@@ -6,7 +6,7 @@ import time
 
 import gi
 gi.require_version('Gst', '1.0')
-from gi.repository import GObject, Gst, GstPbutils
+from gi.repository import Gst, GstPbutils
 
 from mopidy import exceptions
 from mopidy.audio import utils
@@ -193,7 +193,6 @@ if __name__ == '__main__':
 
     from mopidy.internal import path
 
-    GObject.threads_init()
     Gst.init()
 
     scanner = Scanner(5000)

tests/audio/test_actor.py

@@ -5,9 +5,8 @@ import unittest
 
 import gi
 gi.require_version('Gst', '1.0')
-from gi.repository import GObject, Gst
+from gi.repository import Gst
 
-GObject.threads_init()
 Gst.init()
 
 import mock

tests/audio/test_scan.py

@@ -5,9 +5,8 @@ import unittest
 
 import gi
 gi.require_version('Gst', '1.0')
-from gi.repository import GObject, Gst
+from gi.repository import Gst
 
-GObject.threads_init()
 Gst.init()
 
 from mopidy import exceptions