Manifest permissions

Hi there. It seems some more permissions and env. variables have been added/removed over time to the Steam Flatpak. Could you take a look at their manifest to see if you can include/remove new permissions from the Protontricks Flatpak too?

https://github.com/flathub/com.valvesoftware.Steam/blob/beta/com.valvesoftware.Steam.yml (Beta branch I believe)
https://github.com/flathub/com.valvesoftware.Steam/blob/master/com.valvesoftware.Steam.yml (master/stable branch)

And also, something I want to highlight: the network manager permission is not used by them by default. See https://github.com/flathub/com.valvesoftware.Steam/wiki#app-starts-slower-than-native.

Thanks in advance.

Protontricks の Flatpak マニフェストと、beta ブランチおよび master ブランチにあるリンク先の Steam マニフェストファイルを比較します。ネットワークマネージャーの権限を含む、権限と環境変数の違いを確認し、未使用の権限を追加せずに、適切な変更が Protontricks に反映されていることを確認します。

索引モデルが issue の本文から書いたものです。