Remove remnants of separable shader setting (#6403)

src/video_core/video_core.cpp

@@ -24,7 +24,6 @@ std::unique_ptr<RendererBase> g_renderer{}; ///< Renderer plugin
 
 std::atomic<bool> g_shader_jit_enabled;
 std::atomic<bool> g_hw_shader_enabled;
-std::atomic<bool> g_separable_shader_enabled;
 std::atomic<bool> g_hw_shader_accurate_mul;
 
 Memory::MemorySystem* g_memory;