Remove unused dm-bht dependency.

Update engine doesn't use verity for anything. We must use the
statically linked /postinst on the new image to generate the hashes
and we can't use the one on the current image.

This patch removes that unused dependency.

BUG=chromium:380893
TEST=emerge-link update-engine

Change-Id: Ifff63ab324a4cd5ecf8d2fadf23af579e12e70db
Reviewed-on: https://chromium-review.googlesource.com/202634
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
diff --git a/SConstruct b/SConstruct
index 38c396e..532ba68 100644
--- a/SConstruct
+++ b/SConstruct
@@ -156,7 +156,6 @@
 env['LIBS'] = Split("""bz2
                        crypto
                        curl
-                       dm-bht
                        ext2fs
                        gflags
                        glib-2.0