removing spec_res convolution from get_tau
removing spec_res convolution from get_tau

Converting tau to flux and then back to tau is not stable. We get 0 in the `log()` for extended absorbers. If any one is interested in convolving the spectra with spectra resolution, they can call `spec_utils.res_corr()` which works only with flux.
sbird/fake_spectra,sbird/fake_spectra,sbird/fake_spectra