(core) clean up snapshot list when access rules are in effect

Summary:
When access rules are in effect on a document, non-owners currently
don't have access to snapshots. Previously when the document history
tab is opened in this situation, an error toast would appear, along
with a small message that was hard to see in dark mode. This change
removes the toast and improves the message somewhat.

Test Plan: updated test

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D4218

app/server/lib/ActiveDoc.ts

@@ -1715,7 +1715,7 @@ export class ActiveDoc extends EventEmitter {
 
   public async getSnapshots(docSession: OptDocSession, skipMetadataCache?: boolean): Promise<DocSnapshots> {
     if (await this._granularAccess.hasNuancedAccess(docSession)) {
-      throw new Error('cannot confirm access to snapshots');
+      throw new Error('cannot confirm access to snapshots because of access rules');
     }
     return this._docManager.storageManager.getSnapshots(this.docName, skipMetadataCache);
   }