[ML] Remove all rollup code

[jgowdyelastic]

Rollups are being removed in v9.0.
ML still contains some unused code to deal with rollup indices when creating AD and DFA jobs. All of this code needs to be removed.

Relates to https://github.com/elastic/dev/issues/2762 and #193343

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[thomasneirynck]

consider closing, since this seems to be postponed until 10.0

[peteharverson]

Discussed with @jgowdyelastic and we think we may as well carry on and remove the ML rollup code before 10.0. It's unused code, so makes sense to remove it.