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/tr_flares.c

@@ -526,10 +526,6 @@ void RB_RenderFlares (void) {
 		return;		// none visible
 	}
 
-	if ( backEnd.viewParms.isPortal ) {
-		qglDisable (GL_CLIP_PLANE0);
-	}
-
 	Mat4Copy(glState.projection, oldprojection);
 	Mat4Copy(glState.modelview, oldmodelview);
 	Mat4Identity(matrix);