Revert "build.mk: move modules/tests/usr.manifest to build/"

This reverts commit 7555bca3205d0d55f8d0b46f7f90bbee2481471d.

Jaspal writes:

  This commit breaks 'make check' because the location of
  modules/tests/usr.manifest as changed and module.py needs to be
  updated.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>