Problem after merging !244

After merging !244 (merged), bilby.gw.conversion.compute_snrs chokes on

                    signal = ifo.get_detector_response(
                        signal_polarizations,
                        likelihood.waveform_generator.parameters)

because likelhood.waveform_generator.parameters no longer has an ra dec etc.

@colm.talbot, this means that all runs are going to fail with parameter_conversion=bilby.gw.source.lal_binary_black_hole_parameters given to the waveform_generator.

I'm not sure how we should fix this. Should we revert !244 (merged) for now?