Cleanup shader generation code (#10663)

Shader generation is a mess. This commit cleans some parts up, including dropping remains of HLSL support which was never actually implemented.

src/client/clientenvironment.cpp

@@ -51,12 +51,8 @@ class CAOShaderConstantSetter : public IShaderConstantSetter
 
 	~CAOShaderConstantSetter() override = default;
 
-	void onSetConstants(video::IMaterialRendererServices *services,
-			bool is_highlevel) override
+	void onSetConstants(video::IMaterialRendererServices *services) override
 	{
-		if (!is_highlevel)
-			return;
-
 		// Ambient color
 		video::SColorf emissive_color(m_emissive_color);