fix(sidebar): shorten the missing-folder dialog copy (#1145)

The dialog sits in the sidebar and now offers the removal itself, so telling the
user the entries "can still be removed from the sidebar" said the obvious twice
and read oddly next to a button that does exactly that. Say what is true and stop:
"This folder no longer exists on disk. You can remove it from the list."

The result toast follows the button's wording ("removed from the list") instead of
naming the sidebar again. Both strings changed in English, so the existing
translations of them are back in the queue with the new source text rather than
left saying "refresh the sidebar and try again".

static/js/components/SidebarManager.js

@@ -1824,7 +1824,7 @@ export class SidebarManager {
                 );
                 message.textContent = translate(
                     'sidebar.deleteFolderModal.missingMessage', {},
-                    'This folder no longer exists on disk. Its entries can still be removed from the sidebar.'
+                    'This folder no longer exists on disk. You can remove it from the list.'
                 );
                 // There is nothing left to delete, but the records are what keeps
                 // the ghost node in the tree: offer to drop them (issue #1145).