st/egl_g3d: Clean up for x11_drawable_get_depth.

Fix a wrong comment and remove an unnecessary #include.

src/gallium/state_trackers/egl_g3d/x11/x11_screen.c

@@ -52,7 +52,7 @@ struct x11_screen {
    XVisualInfo *visuals;
    int num_visuals;
 
-   /* cached values for x11_drawable_get_format */
+   /* cached values for x11_drawable_get_depth */
    Drawable last_drawable;
    unsigned int last_depth;
 };

src/gallium/state_trackers/egl_g3d/x11/x11_screen.h

@@ -29,7 +29,6 @@
 #include <X11/Xutil.h>
 #include <X11/extensions/dri2tokens.h>
 #include "pipe/p_compiler.h"
-#include "pipe/p_format.h"
 #include "common/native.h"
 
 enum x11_screen_extension {