feat(display): Drop gfx library

Remove the last remaining piece of gfx integration.  With this, the
card10 firmware is now fully rendering using ctx instead!

epicardium/drivers/display/init.c

@@ -19,11 +19,6 @@ Ctx *epicardium_ctx                     = NULL;
 
 void disp_init(void)
 {
-	/*
-	 * This call can be removed once all gfx stuff is replaced.
-	 */
-	display_init_slim();
-
 	/*
 	 * The bootloader has already initialized the display, so we only need
 	 * to do the bare minimum here.