Django Evolution attempts to load test data files containing SQL

statements used to compare the output of various mutations. For

historical reasons, there were two modules that just duplicated the data

from other modules: mysql_old.py and postgresql_pyscopg2.py. The

former may have been due to an older engine (it's not clear when), but

the latter was due to there having once been two similar engines

(postgresql and postgresql_pyscopg2). Those were eventually

consolidated, but have actually been re-introduced in modern versions of

Django.
Either way, those modules were unnecessary. We now map the engine to the

correct test file internally, removing the need for the modules.

Unit tests pass for all engines.