data_collection.py fails with default mass_prior and spin_prior settings

After !35 (merged) if mass_prior == "flat-detector" it changes to "flat-detector-components". But this line is checking if the args contain a valid mass-prior, but does not check for "flat-detector-components", so the default setting will raise a ValueError.

I also suspect this ValueError should be removed because it is (correctly) earlier in the function as well.

Addressed in !42 (closed)