Proto: remove liquidity baking sunset

Context

This MR removes the liquidity baking sunset as it's no longer necessary with the toggle introduced in Jakarta.

Manually testing the MR

Previous protocols have used a sandbox constant of 128 so one could start a sandbox node and bake past the 128th level then verify that the subsidy is still being applied. This is also covered in the existing protocol integration tests.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR