Remove the JS route for locking an entity

Problem/Motivation

The JS method of locking content was added to support the prefetch_cache module see #2916745: Allow for coexistence with the prefetch_cache module. That module attempts to do something quite odd and I think this work-around causes more issues that it solves.

These issues are:

• You can get around content locking by disabling javascript thus defeating the whole purpose of the module.
• #3517183: Content lock create access does not account for content translations
• #3506068: Disable locking on content in trash

Steps to reproduce

See the bug reports

Proposed resolution

Remove the JS - prefetch_cache is an unsupported module. Content translation and the trash module have far more users.

Remaining tasks

User interface changes

Removal of the JS options from the settings form

API changes

TBD.

Data model changes

Removal of the JS options from config.