Remove batch support declaration from block patterns REST, fix navigation areas

[jsnajdr]

Followup to #39185 that removes batch support declaration from the block patterns and categories REST endpoints. They both support only GET, and batching is relevant only for write methods like POST.

I'm also fixing batch support declaration for the /wp/v2/block-navigation-areas endpoints (originally added by @anton-vlasenko in #36374). The /block-navigation-areas endpoint is only readable and doesn't need the declaration. But the /block-navigation-areas/{id} endpoint is writable and doesn't declare batch support. So I moved the declaration to the right place.

How to test:
Before this patch, a batch request like:

await wp.apiFetch( {
  path: '/batch/v1',
  method: 'POST',
  data: {
    requests: [ {
      path: '/wp/v2/block-navigation-areas/1'
    } ]
  }
} )

would fail with a rest_batch_not_allowed error. After this patch, it fails with rest_navigation_area_invalid which is better: the batch is performed, and it's the 1 id that's deemed invalid.

[ntsekouras]

LGTM, thanks!