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_shadows.c

@@ -261,7 +261,6 @@ void RB_ShadowFinish( void ) {
 	qglEnable( GL_STENCIL_TEST );
 	qglStencilFunc( GL_NOTEQUAL, 0, 255 );
 
-	qglDisable (GL_CLIP_PLANE0);
 	GL_Cull( CT_TWO_SIDED );
 
 	GL_BindToTMU( tr.whiteImage, TB_COLORMAP );