vboot: Stop compiling in the old code which composed screens in depthcharge.

This code is left in the repository since it shows how to construct the
screens once a new scheme has been put in place. Since it relies on the old
graphics stack however, it won't compile in the near future.

Change-Id: Id7d8c9c4617a98c591b63e8f9021cacbf7d4ed7e
diff --git a/src/vboot/Makefile.inc b/src/vboot/Makefile.inc
index 9eab94b..9b475da 100644
--- a/src/vboot/Makefile.inc
+++ b/src/vboot/Makefile.inc
@@ -19,7 +19,6 @@
 
 depthcharge-y += stages.c
 depthcharge-y += firmware_id.c
-depthcharge-y += screens.c
 depthcharge-y += vbnv.c
 
 VB_LIB = $(obj)/external/vboot/vboot_fw.a