Revert to installing steam as a .deb package

Flatpak seems to complicate Steam's execution of Proton

overlay/etc/supervisor.d/steam.ini

@@ -10,8 +10,7 @@ autorestart=true
 startretries=50
 user=%(ENV_USER)s
 directory=/home/%(ENV_USER)s
-# command=/usr/games/steam -bigpicture
-command=/usr/games/steam
+command=/usr/games/steam %(STEAM_ARGS)s
 environment=HOME="/home/%(ENV_USER)s",USER="%(ENV_USER)s",DISPLAY="%(ENV_DISPLAY)s"
 stopsignal=INT
 stdout_logfile=/home/%(ENV_USER)s/.cache/log/steam.log