Gamemode integration broken - requires usage of gamemode portal

Since d6aa13bebec5db68533af5aae262f2c560910571784d324e8b25d56c2a4d82bb (2f45a317f2a6573b7f44635ac8c808f1f467f35b) Steam fails to launch games with Proton when Mangohud is enabled, they just get stuck on the 'Preparing to launch' window.
Downgrading to 7325dcb0102b06e1706dd99a7e465be0b4d6846a04b5b6bb9003a480fa8e88ae (104142dac236e427d042f3726221842c10a81f02) makes them work again.
The log doesn't seem to contain anything useful besides the `glxinfo: not found` mentioned in #2
```
GameAction [AppID 230410, ActionID 3] : LaunchApp changed task to ProcessingInstallScript with ""
esync: up and running.
wine: RLIMIT_NICE is <= 20, unable to use setpriority safely
WARNING: radv is not a conformant Vulkan implementation, testing use only.
[2021-12-20 14:36:39.380] [MANGOHUD] [info] [config.cpp:114] skipping config: '/home/j/.var/app/com.valvesoftware.Steam/config/MangoHud/wine-explorer.conf' [ not found ]
[2021-12-20 14:36:39.380] [MANGOHUD] [info] [config.cpp:114] skipping config: '/home/j/Games/Steam/steamapps/common/Proton - Experimental/files/bin/MangoHud.conf' [ not found ]
[2021-12-20 14:36:39.380] [MANGOHUD] [info] [config.cpp:114] skipping config: '/home/j/.var/app/com.valvesoftware.Steam/config/MangoHud/wine64-preloader.conf' [ not found ]
[2021-12-20 14:36:39.380] [MANGOHUD] [info] [config.cpp:119] parsing config: '/home/j/.var/app/com.valvesoftware.Steam/config/MangoHud/MangoHud.conf'
[2021-12-20 14:36:39.382] [MANGOHUD] [error] [dbus_helpers.h:344] [send_with_reply_and_block]: org.freedesktop.DBus.Error.ServiceUnknown
sh: 1: glxinfo: not found
```