Simplify parsing LTI objects
This PR simplifies the handling of scipy.signal.LinearTimeInvariant
objects in gwpy.signal.filter_design
; the change in #1484 doesn't actually work with scipy-1.8.0.
This PR simplifies the handling of scipy.signal.LinearTimeInvariant
objects in gwpy.signal.filter_design
; the change in #1484 doesn't actually work with scipy-1.8.0.