Remove the Navigation top bar from the entity override builder

Problem/Motivation

Part of #3624760: Plan: consistent Display Builder entry points in the Navigation top bar.

#3543335: Navigation top bar not present on entity overrides registers a display_builder_override.VIEW_MODE link template per view mode, so Navigation treats /node/{node}/display/{mode} as a content entity route and shows its top bar. The three other builders are admin routes and have no top bar. The override builder is the odd one out, and the top bar stacks on top of the builder's own toolbar and Back button.

Proposed resolution

Revert #3543335: Navigation top bar not present on entity overrides: remove the link templates from display_builder_entity_view/src/Hook/Navigation.php. No builder shows the top bar until #3529095: Adopt navigation module's top bar integrates both.

Remaining tasks

• Check nothing else reads the display_builder_override.* link templates.
• Test: no top bar on the override builder.