bayestar_localize_coincs: omit method strings from filenames
requested to merge leo-singer/lalsuite:bayestar-localize-coincs-shorter-output-filenames into master
The script bayestar_localize_coincs indicates the sky localization
method in output filenames with suffixes like .toa_phoa_snr.fits
or .toa_phoa_snr_mcmc.fits.
However, it is very rare to actually run BAYESTAR with any but the
default localization method (toa_phoa_snr). In the interest of
shorter and more readable filenames, let's omit the method suffix
if the user only requests one method.