pybrial: 1.2.3 -> 1.2.5, directly use the brial src

The pybrial package is a bit awkward. It doesn't have its own top-level
attribute, since it has a cyclic dependency with sage. That's one of the
reasons why it rarely gets updated. Its distributed along with brial, so
its best to keep the versions synchronized. The easiest way to do this
is to just re-use the source of brial.