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_extensions.c

@@ -30,7 +30,7 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 #include "tr_local.h"
 #include "tr_dsa.h"
 
-void GLimp_InitExtraExtensions()
+void GLimp_InitExtraExtensions(void)
 {
 	char *extension;
 	const char* result[3] = { "...ignoring %s\n", "...using %s\n", "...%s not found\n" };