OpenGL2: Misc fixes and cleanup

Fix two constants in GLSL shaders. Remove f suffix from float and fix
int to float assignment. They were causing shader compile errors in
OpenGL ES 2 context.

Remove disabling clip plane. Clip plane is unused and never enabled in
the opengl2 renderer. Remove disabling it to avoid causing a GL error
when using OpenGL 3.2 core profile or OpenGL ES.

Make VAO cache vertex stride be size of srfVert_t since that is what
is uploaded to the GPU. No behavior change. There is a disabled debug
id in srfVert_t though which if enabled changes srfVert_t size.

code/renderergl2/glsl/calclevels4x_fp.glsl

@@ -56,5 +56,5 @@ void main()
 	current.y *= 0.0625;
 #endif
 
-	gl_FragColor = vec4(current, 1.0f);
+	gl_FragColor = vec4(current, 1.0);
 }