Baker: remove agnostic

Closes #7904 (closed)

This is a subset of what has been done to remove the experimental in !17491 (merged).

The idea is to remove agnostic from what's visible for users, internally we can keep using agnostic baker it's fine, therefore I didn't change the path internally, the constant names etc. This is debatable, I followed a bit the same practice as for smart contract rollup, most of the code (especially in the protocol) are named sc_rollup_something*, but to the outside world we name it smart_rollup.