[Enhancement]: Remove useless metadata table `_timescaledb_catalog.continuous_aggs_bucket_function`

[fabriziomello]

What type of enhancement is this?

Tech debt reduction

What subsystems and features will be improved?

Continuous aggregate

What does the enhancement do?

Remove useless metadata table _timescaledb_catalog.continuous_aggs_bucket_function. This table is not necessary anymore because we already refactored the current code to get the bucket function Oid based on the query tree stored on Postgres metadata (https://github.com/timescale/timescaledb/pull/7042).

Implementation challenges

No response