Remove lportal module

This is available in Godot 3.x now, see godotengine/godot#46130.

[ci skip]

.gitmodules

@@ -26,10 +26,6 @@
 	path = modules/voxel
 	url = https://github.com/Zylann/godot_voxel
 	branch = godot3.3
-[submodule "lportal"]
-	path = modules/lportal
-	url = https://github.com/lawnjelly/godot-lportal
-	branch = master
 [submodule "llightmap"]
 	path = modules/llightmap
 	url = https://github.com/lawnjelly/godot-llightmap

README.md

@@ -28,7 +28,6 @@ as it may not be actively updated.
 | [goost](https://github.com/goostengine/goost)                         | A general-purpose C++ extension for Godot.     | ✔            |
 | [json](https://github.com/godot-extended-libraries/json)              | Import JSON files as resources.                | ✔            |
 | [llightmap](https://github.com/lawnjelly/godot-llightmap)             | Soft shadows with high performance at runtime. | ❌            |
-| [lportal](https://github.com/lawnjelly/godot-lportal)                 | Portal rendering and culling.                  | ✔            |
 | [qurobullet](https://github.com/quinnvoker/qurobullet)                | Design 2D projectile system.                   | ❌            |
 | [smooth](https://github.com/lawnjelly/godot-smooth)                   | Fixed timestep interpolation helper nodes.     | ❌            |
 | [sqlite](https://github.com/godot-extended-libraries/godot-sqlite)    | SQLite for Godot based on gdsqlite-native.     | ✔            |