Use OpenGL 3.3 core profile instead of compatibility profile

- Rename OpenGL to GLES3 in the source code per community feedback.
  - The renderer is still exposed as "OpenGL 3" to the user.
- Hide renderer selection dropdown until OpenGL support is more mature.
  - The renderer can still be changed in the Project Settings or using
    the `--rendering-driver opengl` command line argument.
- Remove commented out exporter code.
- Remove some OpenGL/DisplayServer-related debugging prints.

platform/linuxbsd/detect.py

@@ -381,7 +381,7 @@ def configure(env):
             # No pkgconfig file for glslang so far
             env.Append(LIBS=["glslang", "SPIRV"])
 
-    env.Append(CPPDEFINES=["OPENGL_ENABLED"])
+    env.Append(CPPDEFINES=["GLES3_ENABLED"])
     env.Append(LIBS=["GL"])
 
     env.Append(LIBS=["pthread"])