[ENH] Revise datasets in datasets/data

[TonyBagnall]

Describe the feature or idea you want to propose

the size of the package is growing, and a lot of this is in the shipped datasets, a lot of which are there for legacy reasons.

Related to this re PLAID #2224

Describe your proposed solution

We should go through and consider if we can ditch or replace any.

Collections:
ACSF1, ArrowHead, BasicMotions., CardanoSentiment, Covid3Months, GunPoint, ItalyPowerDemand, JapaneseVowels, OSULeaf, PLAID, UnitTest

Series for forecasting:
Airline, Longley, Lunx, m1_yearly_dataset, PBS_dataset, solar, Uschange

Others
Daphnet_SO6RO2EO
KDD_TSAD_135

Describe alternatives you've considered, if relevant

No response

Additional context

No response