Revert "feat: native smart tags (#782)"

This reverts commit c3772e06b4.

app/assets/javascripts/strings.ts

@@ -22,8 +22,6 @@ export const STRING_NEW_UPDATE_READY =
 export const STRING_DELETE_TAG =
   'Are you sure you want to delete this tag? Note: deleting a tag will not delete its notes.';
 
-export const STRING_MISSING_SYSTEM_TAG = 'We are missing a System Tag.';
-
 /** @editor */
 export const STRING_SAVING_WHILE_DOCUMENT_HIDDEN =
   'Attempting to save an item while the application is hidden. To protect data integrity, please refresh the application window and try again.';