Refactor H2 star formation parameters

[bwkeller]

When COOLING_MOLECULARH is enabled, an additional parameter is added, dStarFormEfficiencyH2. This parameter behaves both like a boolean to enable or disable H2-based efficiencies (1 or 0 respectively) but also acts as a multiplicative factor on dCStar as well. If a user presumes that this is the H2 version of dCStar, they will end up with an efficiency parameter that is 5% what they expect, as it will be multiplied by the default value of dCStar (0.05). We should change this to a boolean parameter, bStarFormEfficiencyH2, and remove it from the calculation of the efficiency (just use it as a switch).

[trquinn]

@CharlotteRuth this was originally implemented in GASOLINE with the following comment:

double dStarFormEfficiencyH2; /* Star formation efficiency, CStar, is multiplied by dStarFormEfficiencyH2 times the fraction of hydrogen in molecular form  */

Was there a reason to have this parameter be degenerate with CStar?