Removed level compilers and corresponding dependencies

1. They were almost untested and not properly supported
2. We plan to bring a new life to SDK and tools, but that will come much later, when engine features will be ready.
I'm really in favor of SkyLoader's universal compilers, use them.
https://ap-pro.ru/forums/topic/3341-universalnye-kompilyatory-urovney-h64/
https://igigog.github.io/anomaly-modding-book/modding-tools/universal-x64-level-compilers.html

This also accidentally closes #49 as hxGrid was a dependency for xrLC only which was removed, hence we have removed hxGrid too.

Author: Xottab-DUTY

.gitmodules

@@ -31,9 +31,6 @@
 [submodule "Externals/OpenAutomate"]
 	path = Externals/OpenAutomate
 	url = https://github.com/OpenXRay/OpenAutomate.git
-[submodule "Externals/FreeMagic"]
-	path = Externals/FreeMagic
-	url = https://github.com/OpenXRay/FreeMagic.git
 [submodule "Externals/gli"]
 	path = Externals/gli
 	url = https://github.com/g-truc/gli.git

Externals/CMakeLists.txt

@@ -14,7 +14,6 @@ endif()
 add_subdirectory(GameSpy)
 add_subdirectory(OPCODE)
 add_subdirectory(ode)
-#add_subdirectory(NVTT)
 add_subdirectory(imgui-proj)
 
 if (NOT TARGET xrLuabind)