Remove anyjson package

This is no longer required by Celery [1] and now causes an error
when deploying with the new versions of other packages:

        use_2to3 is invalid

[1]: https://docs.celeryproject.org/en/stable/history/whatsnew-4.0.html#requirements

requirements.txt

@@ -47,7 +47,6 @@ gds-metrics==0.2.4
 ## The following requirements were added by pip freeze:
 alembic==1.7.4
 amqp==5.0.6
-anyjson==0.3.3
 attrs==21.2.0
 awscli==1.21.4
 bcrypt==3.2.0