Remove assert forms only present in Python 2.7.
Remove assert forms only present in Python 2.7.


Former-commit-id: aa2b026264f5d0186c80a5bcd2c08fc235626072 [formerly 89bd13c2264636eae04e66082e70ad95d5b73abd]
Former-commit-id: 5f04b1c117eca3918f54de0d83e35e91e7d6b7e9
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine