Remove obsolete encode/decode calls

[ghost]

This fixes the following error I'm seeing when I try to add URIs to the playlist on the current master version:

Traceback (most recent call last):
  File "/home/user/Projects/syncplay/syncplay/ui/gui.py", line 628, in <lambda>
    menu.addAction(QtGui.QPixmap(resourcespath + "world_add.png"), getMessage("addurlstoplaylist-menu-label"), lambda: self.OpenAddURIsToPlaylistDialog())
  File "/home/user/Projects/syncplay/syncplay/ui/gui.py", line 382, in wrapper
    return f(self, *args, **kwds)
  File "/home/user/Projects/syncplay/syncplay/ui/gui.py", line 979, in OpenAddURIsToPlaylistDialog
    URI = urllib.parse.unquote(URI)
  File "/usr/lib64/python3.6/urllib/parse.py", line 610, in unquote
    if '%' not in string:
TypeError: a bytes-like object is required, not 'str'

[albertosottile]

Tested this on macOS, it solves the bug. Thank you for spotting and patching this.

[Et0h]

I've confirmed the bug and the fix. Thank you for your contribution :)