Remove python-anyjson dependency

Version 0.3.3 of this dependency is available in RHEL6, RHEL7 and Fedora. We no
longer need to carry it.
Merge pull request #1455 from mhrivnak/1174353

1174353 - improving performance of "pulp-admin tasks list
Merge pull request #1456 from beav/no-anyjson

Remove python-anyjson dependency
Merge remote-tracking branch 'origin/2.6-dev'