Revert "sway: Use workspace 6 as default for zathura"

This reverts commit 681a979fba.

Allow Zathura to be opened in any workspace. Fixed workspace
is restrictive.

sway/.config/sway/config.d/70-app.conf

@@ -7,6 +7,5 @@ for_window [app_id="gst-launch-1.0"] floating enable, resize set width 1920 px h
 assign [app_id="gst-launch-1.0"] 5
 assign [title="gst-play-1.0"] 5
 assign [app_id="mpv"] 6
-assign [app_id="org.pwmt.zathura"] 6
 assign [app_id="vimiv"] 8
 assign [app_id="xdot"] 8