chore: remove four modules nothing in the app uses (#1403)

* chore: remove four modules nothing in the app uses

src/app/sourceSlot.js re-exported src/sources/sourceSlot.js, which every
caller imports directly. src/data/flowTiles.js and src/data/issPass.js were
reached only by their own tests. src/data/localGeojson.js wrapped
localGeojsonCore.js with the app's services, which the catalog already
passes itself. The local GeoJSON layer tests now build layers the way the
catalog does, so they keep covering localGeojsonCore.js; only the test of
the wrapper's own default host goes. Boundary lists, format scope and docs
drop the removed paths.

* docs: changelog for #1403

src/app/sourceSlot.js

@@ -1,2 +0,0 @@
-// Compatibility entry; source contracts are owned by sources/.
-export { createSourceSlot } from '../sources/sourceSlot.js';

src/app/sourceSlot.test.mjs

@@ -1,24 +0,0 @@
-import test from 'node:test';
-import assert from 'node:assert/strict';
-import { createSourceSlot } from './sourceSlot.js';
-
-test('replacing a source rejects its late result and old cleanup cannot clear the new source', async () => {
-  let finish;
-  const slot = createSourceSlot({ read: async () => 'default' }, ['read']);
-  const old = slot.configure({ read: () => new Promise(resolve => { finish = resolve; }) });
-  const pending = slot.source.read();
-  const stop = slot.configure({ read: async () => 'replacement', attribution: { name: 'Replacement' } });
-  old();
-  finish('stale');
-  await assert.rejects(pending, { name: 'AbortError' });
-  assert.equal(await slot.source.read(), 'replacement');
-  assert.equal(slot.source.attribution.name, 'Replacement');
-  stop();
-  assert.throws(() => slot.source.read(), /not configured/);
-});
-
-test('an invalid replacement leaves the working source intact', async () => {
-  const slot = createSourceSlot({ read: async () => 42 }, ['read']);
-  assert.throws(() => slot.configure({}), TypeError);
-  assert.equal(await slot.source.read(), 42);
-});