Revert "Keep a place, and come back to it"

This reverts commit bd3a5a4. The bookmarks work was committed onto this branch
by mistake — it belongs to its own pull request, and it has one, branched from
this branch's own tip. Reverting rather than rewinding because the branch is
published and a pull request is open against it: the diff this pull request
shows is what matters, and after this it shows the routing change alone.

src/app/shared/ui/bookmark-icon.component.ts

@@ -1,22 +0,0 @@
-import { ChangeDetectionStrategy, Component, input } from '@angular/core';
-
-/**
- * The mark on a place worth coming back to. Hollow when it is not kept, filled when it is —
- * the same two states as the Display panel's layer ticks, which is where the eye has already
- * learned what a filled mark means here.
- *
- * Size and colour come from the classes on the host; the svg fills it.
- */
-@Component({
-  selector: 'app-bookmark-icon',
-  changeDetection: ChangeDetectionStrategy.OnPush,
-  host: { class: 'block', 'aria-hidden': 'true' },
-  template: `
-    <svg class="h-full w-full" viewBox="0 0 24 24" [attr.fill]="kept() ? 'currentColor' : 'none'" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round">
-      <path d="M7 4h10v16l-5-4-5 4z" />
-    </svg>
-  `
-})
-export class BookmarkIconComponent {
-  readonly kept = input(false);
-}