buildd: Re-enable merged /usr by default, as it is now required

Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>

live-build/auto/config

@@ -1257,11 +1257,6 @@ esac
 case $SUBPROJECT in
 	buildd)
 		cp -af /usr/share/livecd-rootfs/live-build/buildd/* config/
-
-		# Disable merged /usr to avoid building packages with
-		# hardcoded paths that assume it.
-		echo 'DEBOOTSTRAP_OPTIONS="$DEBOOTSTRAP_OPTIONS --no-merged-usr"' \
-			>> config/common
 		;;
 esac