Tests for the`montecarlo` part of the code needs to be revised

[DhruvSondhi]

Describe the bug The tests for the montecarlo part of the code present in tardis/monteacarlo/tests/test_montecarlo.py have an outdated docstring pertaining to testing being done in C part of the code. But as the C part of the code has been removed, the tests needs to be revised & changed for the updated numba based implementation Tests present here - https://github.com/tardis-sn/tardis/blob/master/tardis/montecarlo/tests/test_montecarlo.py