Powermock was introduced in I5a38a5fd3, but is not used in any of the
core tests or core plugins' tests. It is however used by some non-core
plugins (for example its-base, its-phabricator, owners) and those will
need to be migrated away from powermock, as was already done for the
slack-integration plugin in change I7595a8359, or explicitly add it to
their external dependencies.
Also remove javassist which was added as a transitive dependency at the
same time powermock was added.
Feature: Issue 5057
Change-Id: Iafcc40d2fafa58b9262b318d0207cff99239bd15
da3b9e1694