[client] egl: remove dependency on SDL

After this PR, EGL functions are now accessed through <EGL/egl.h>
instead of through <SDL2/SDL_egl.h>, removing a pointless dependency
on SDL.

client/renderers/EGL/shader.c

@@ -25,8 +25,6 @@ Place, Suite 330, Boston, MA 02111-1307 USA
 #include <string.h>
 #include <stdio.h>
 
-#include <SDL2/SDL_egl.h>
-
 struct EGL_Shader
 {
   bool   hasShader;