gl_state: Remove unused type alias

This isn't used anywhere within the header, so we can remove it, along
with the include that was previously necessary. This also uncovers an
indirect include in the cpp file for the assertion macros.

src/video_core/renderer_opengl/gl_state.cpp

@@ -4,6 +4,7 @@
 
 #include <iterator>
 #include <glad/glad.h>
+#include "common/assert.h"
 #include "common/logging/log.h"
 #include "video_core/renderer_opengl/gl_state.h"
 

src/video_core/renderer_opengl/gl_state.h

@@ -7,12 +7,8 @@
 #include <array>
 #include <glad/glad.h>
 
-#include "video_core/engines/maxwell_3d.h"
-
 namespace OpenGL {
 
-using Regs = Tegra::Engines::Maxwell3D::Regs;
-
 namespace TextureUnits {
 
 struct TextureUnit {