Stop generating the Delete local task

From the comment I made in the core issue (#2976861: add an entity Links handler, to provide menu links/tasks/actions for entity types):

One interesting note: This code currently always generates a Delete local task.

However, core only provides a Delete local task for content entities. Delete local tasks for config entities were explicitly removed in #1834002: Configuration delete operations are all over the place. I am guessing that we don't want to revert that conclusion. So we should either define the Delete local task only for content entity types, or never.

So, our DefaultEntityLocalTaskProvider should either generate the Delete local task for content entities only, or never.