Remove sidebar "content preview" checkbox

Problem/Motivation

With Gin LB there are two different ways of enabling the content preview - the options in the toolbar button and the "Show content preview" checkbox in the sidebar. This is redundant.

Proposed resolution

Remove the "Show content preview" checkbox in the sidebar.

Remaining tasks

Decide on whether this is the correct approach.
Provide a patch / MR with the change.

User interface changes

There wouldn't be a "Show content preview" option in the sidebar.

API changes

TBD

Data model changes

TBD