DEPR: remove deprecated method `is_anchored`
xref #56594

removed deprecated methods `DateOffset.is_anchored` and `offsets.Tick.is_anchored`
I enforced the deprecation of `DateOffset.is_anchored` and `offsets.Tick.is_anchored`. @MarcoGorelli, could you please take a look at this PR? I think, CI failures are not related to my changes. Thanks @MarcoGorelli for reviewing this PR. 