Remove obsolete FindDirectX.cmake script

There's no need to find DirectX because with VS2013 and mingw it's
already available by default.  Older visual studio versions that didn't
come with DirectX by default are no longer supported anyway.

(Also mingw doesn't currently work at all due to lack of proper headers,
but once they do it'll be available in the same way.  I think.)

libobs-d3d11/CMakeLists.txt

@@ -2,13 +2,6 @@ project(libobs-d3d11)
 
 include_directories(SYSTEM "${CMAKE_SOURCE_DIR}/libobs")
 
-find_package(DirectX REQUIRED)
-if(NOT DirectX_D3D11_FOUND)
-	message(FATAL_ERROR "No D3D11 SDK Found!")
-endif()
-include_directories(
-	${DirectX_D3D11_INCLUDE_DIRS})
-
 add_definitions(-DLIBOBS_EXPORTS)
 
 set(libobs-d3d11_SOURCES
@@ -35,9 +28,8 @@ set_target_properties(libobs-d3d11
 		PREFIX "")
 target_link_libraries(libobs-d3d11
 	libobs
-	${DirectX_LIBRARY}
-	${DirectX_DXGI_LIBRARY}
-	${DirectX_D3DCOMPILER_LIBRARY}
-	${DirectX_D3D11_LIBRARIES})
+	d3d11
+	dxgi
+	d3dcompiler)
 
 install_obs_core(libobs-d3d11)