deja-dup: fix fusermount error

Currently the Meson option `fusermount_command` is set to a path in the Nix store, but `fusermount` requires setuid, so when trying to mount a restic backup, it fails with `fusermount: mount failed: Operation not permitted`. This commit instead patches deja-dup's `find-fusermount` script to use the setuid wrapper `/run/wrappers/bin/fusermount` if it exists.

I also switched the package from using fuse2 to fuse3 because both are supported and I didn't see a reason to use the older version.

pkgs/by-name/de/deja-dup/find-fusermount-setuid.patch

@@ -0,0 +1,13 @@
+diff --git a/libdeja/find-fusermount b/libdeja/find-fusermount
+index 1b3211bb..95b35cf5 100755
+--- a/libdeja/find-fusermount
++++ b/libdeja/find-fusermount
+@@ -20,6 +20,8 @@
+ if [ ! -f /.flatpak-info ]; then
+   if [ -n "@FUSERMOUNT_CMD@" ]; then
+     echo "@FUSERMOUNT_CMD@"
++  elif [ -f /run/wrappers/bin/fusermount3 ]; then
++    echo /run/wrappers/bin/fusermount3
+   elif command -pv fusermount3 > /dev/null; then
+     command -pv fusermount3
+   elif command -pv fusermount > /dev/null; then

pkgs/by-name/de/deja-dup/package.nix

@@ -21,7 +21,6 @@
   json-glib,
   borgbackup,
   duplicity,
-  fuse,
   rclone,
   restic,
   nix-update-script,
@@ -66,7 +65,6 @@ stdenv.mkDerivation (finalAttrs: {
     # Check https://gitlab.gnome.org/World/deja-dup/-/blob/main/meson.options
     (lib.mesonOption "borg_command" (lib.getExe borgbackup))
     (lib.mesonOption "duplicity_command" (lib.getExe duplicity))
-    (lib.mesonOption "fusermount_command" (lib.getExe' fuse "fusermount"))
     (lib.mesonOption "rclone_command" (lib.getExe rclone))
     (lib.mesonOption "restic_command" (lib.getExe restic))
     (lib.mesonEnable "packagekit" false) # packagekit-glib not packaged
@@ -79,6 +77,8 @@ stdenv.mkDerivation (finalAttrs: {
     )
   '';
 
+  patches = [ ./find-fusermount-setuid.patch ];
+
   passthru = {
     updateScript = nix-update-script { };
   };