Vulkan: Remove MoltenVK

Blender had some support for using MoltenVK. However there are some key
issues why MotlenVK cannot be used. Bugs have been reported up-stream.
As it doesn't work and holds back regular developments it will be removed
from the main branch.

Any efforts on making Vulkan run on Apple (including KosmicKrisp)
is considered a community effort and can be done in a development
branch.

Pull Request: https://projects.blender.org/blender/blender/pulls/144602

CMakeLists.txt

@@ -956,22 +956,12 @@ else()
 endif()
 
 # Vulkan
-option(WITH_VULKAN_BACKEND "Enable Vulkan as graphics backend (experimental)" ON)
-mark_as_advanced(WITH_VULKAN_BACKEND)
-if(APPLE)
-  option(WITH_VULKAN_MOLTENVK "Enable Vulkan over MoltenVK (development option)" OFF)
-  mark_as_advanced(WITH_VULKAN_MOLTENVK)
-endif()
-
-if(APPLE AND NOT WITH_VULKAN_MOLTENVK)
+if(NOT APPLE)
+  option(WITH_VULKAN_BACKEND "Enable Vulkan as graphics backend" ON)
+  mark_as_advanced(WITH_VULKAN_BACKEND)
+else()
   set(WITH_VULKAN_BACKEND OFF)
 endif()
-if(NOT WITH_EXPERIMENTAL_FEATURES)
-  if(APPLE)
-    set(WITH_VULKAN_MOLTENVK OFF)
-    set(WITH_VULKAN_BACKEND OFF)
-  endif()
-endif()
 
 # Metal
 if(APPLE)