Remove deprecated code from before TSF v5.1

[sybrew]

In TSF v5.0, released on November 22, 2023, we were left with over 420 deprecations:

1. 388 methods
2. 4 classes
3. 11 properties
4. 35 filters
5. 1 action

Purging them will ease maintenance and reduce the plugin's size by about 10%.

If we remove the deprecated classes, sites could experience crashes — we currently handle these via class extensions.

Automated deprecation handlers account for methods and properties; still, removing those could result in unexpected values being returned to the caller. Here are all deprecated methods.

Filters and action removal should only affect behavior; probably, no one will notice that.

We'll see TSF v5.2 in Summer 2025 at the earliest. A 1.5-year window would be plenty for migrations; I also offered to update all deprecated code any user would have, and that offer still stands.