Remove defaults for coinc_far

I ran into errors in using coinc_far since I assumed given some parameters it would pick correctly, but forgot to specify the joint_far_methdod . I ended getting errors because it picked untargeted when I meant to use the targeted method, which was indicated by the default parameters.

Remove GRB and Fermi from this line: https://git.ligo.org/lscsoft/raven/-/blob/45fd781160edde6460c2583ef9b114e8c34c1c3c/ligo/raven/search.py#L444