support metamodule, remove built-in overlayfs mount

Co-authored-by: weishu <twsxtd@gmail.com>
Co-authored-by: YuKongA <70465933+YuKongA@users.noreply.github.com>
Co-authored-by: Ylarod <me@ylarod.cn>

userspace/meta-overlayfs/metamodule/uninstall.sh

@@ -0,0 +1,24 @@
+#!/system/bin/sh
+############################################
+# mm-overlayfs uninstall.sh
+# Cleanup script for metamodule removal
+############################################
+
+MODDIR="${0%/*}"
+MNT_DIR="$MODDIR/mnt"
+
+echo "- Uninstalling metamodule..."
+
+# Unmount the ext4 image if mounted
+if mountpoint -q "$MNT_DIR" 2>/dev/null; then
+    echo "- Unmounting image..."
+    umount "$MNT_DIR" 2>/dev/null || {
+        echo "- Warning: Failed to unmount cleanly"
+        umount -l "$MNT_DIR" 2>/dev/null
+    }
+    echo "- Image unmounted"
+fi
+
+echo "- Uninstall complete"
+
+exit 0