compositor-{drm, x11, wayland}: stop including EGL headers here

Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/src/gl-renderer.h b/src/gl-renderer.h
index c5550d1..d4da567 100644
--- a/src/gl-renderer.h
+++ b/src/gl-renderer.h
@@ -27,6 +27,7 @@
 #ifdef ENABLE_EGL
 
 #include <EGL/egl.h>
+#include <EGL/eglext.h>
 
 #else