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

changelog.d/1403-remove-unused-modules.md

@@ -0,0 +1,5 @@
+- Remove four modules nothing in the app imports: `src/app/sourceSlot.js`,
+  `src/data/flowTiles.js`, `src/data/issPass.js` and `src/data/localGeojson.js`.
+  The local GeoJSON layer tests now build layers the way the catalog does, so
+  they keep covering `localGeojsonCore.js`. Package exports are unchanged
+  (samehkhamis, #1403).