tor-browser: remove unnecessary auto-update policies

This came up in Firefox as
https://bugzilla.mozilla.org/show_bug.cgi?id=2042197, where policies
caused different behavior to be active (also see
https://github.com/NixOS/nixpkgs/pull/524793). We should not observe any
such differences, but this indicates that the policy is unnecessary for
disabling the updater.

Tor/Mullvad Browser have supported is-packaged-app for a long time
(https://gitlab.torproject.org/tpo/applications/tor-browser/-/merge_requests/985),
and it's preferred by Firefox (i.e. it actually has meaning there:
https://searchfox.org/firefox-main/search?q=is-packaged-app&path=&case=false&regexp=false), so we switch from `system-install` to that one. This shouldn't
change anything else user visible.

This removes the "Your browser is being managed by your organization."
text from about:preferences and changes about:policies from showing this
singular policy to "The Enterprise Policies service is inactive." (the
intended upstream behavior), so this seems like a win for clarity.

Tested by downgrading the version in the derivation, and seeing no
update UI appear, either in the hamburger menu in the toolbar or under
Help > About Tor Browser.

pkgs/by-name/to/tor-browser/package.nix

@@ -136,12 +136,6 @@ let
       };
     }
   );
-
-  policiesJson = writeText "policies.json" (
-    builtins.toJSON {
-      policies.DisableAppUpdate = true;
-    }
-  );
 in
 stdenv.mkDerivation rec {
   pname = "tor-browser";
@@ -213,8 +207,8 @@ stdenv.mkDerivation rec {
     # firefox is a wrapper that checks for a more recent libstdc++ & appends it to the ld path
     mv firefox.real firefox
 
-    # store state at `~/.tor browser` instead of relative to executable
-    touch "$TBB_IN_STORE/system-install"
+    # store state at `~/.tor project` instead of relative to executable
+    touch "$TBB_IN_STORE/is-packaged-app"
 
     # The final libPath.  Note, we could split this into firefoxLibPath
     # and torLibPath for accuracy, but this is more convenient ...
@@ -331,7 +325,6 @@ stdenv.mkDerivation rec {
 
     # Install distribution customizations
     install -Dvm644 ${distributionIni} $out/share/tor-browser/distribution/distribution.ini
-    install -Dvm644 ${policiesJson} $out/share/tor-browser/distribution/policies.json
 
     runHook postInstall
   '';