kokoro: Fix the rootfs build

We no longer have a git/continuous-build directory.

Change-Id: I2cfe0ee9c48a97d2f6927af0a5bcd8f51db6edda
diff --git a/kokoro/rootfs.sh b/kokoro/rootfs.sh
index 089a836..510005e 100644
--- a/kokoro/rootfs.sh
+++ b/kokoro/rootfs.sh
@@ -2,8 +2,7 @@
 
 set -e
 
-pushd git/continuous-build
-ln -srf build/Makefile .
+pushd git
 source build/setup.sh
 popd