[plugin_installer] Revert last version update

plugin_installer/manifest.ini

 [info]
 name: Plugin Installer
 short_name: plugin_installer
-version: 0.20.5
+version: 0.20.4
 description: Install and upgrade plugins from ftp
 authors: Denis Fomin <fominde@gmail.com>
  Yann Leboulanger <asterix@lagaule.org>

plugin_installer/plugin_installer.py

@@ -55,12 +55,6 @@ except ImportError:
     from gajim.dialogs import WarningDialog, HigDialog, YesNoDialog
     from gajim.gtkgui_helpers import get_action
 
-# Since Gajim 1.1.0 _() has to be imported
-try:
-    from gajim.common.i18n import _
-except ImportError:
-    pass
-
 log = logging.getLogger('gajim.plugin_system.plugin_installer')
 
 PLUGINS_URL = 'https://ftp.gajim.org/plugins_1/'