Remove now unused Vulkan-Docs submodule

.gitmodules

@@ -42,10 +42,6 @@
 [submodule "External/xxhash"]
 	path = External/xxhash
 	url = https://github.com/FEX-Emu/xxHash.git
-[submodule "External/Vulkan-Docs"]
-  shallow = true
-	path = External/Vulkan-Docs
-	url = https://github.com/KhronosGroup/Vulkan-Docs.git
 [submodule "External/Catch2"]
 	path = External/Catch2
 	url = https://github.com/catchorg/Catch2.git