Eliminate an unnecessary AsMutable() call in BookmarkModel::RemoveNodeAndGetRemovedUrls()

BookmarkModel::RemoveNodeAndGetRemovedUrls() does not require AsMutable
as sunction itself suggest RemoveNode and get its url, and parent() can
return non const pointer. So AsMutable() is not required in this case.

BUG=481500

Review URL: https://codereview.chromium.org/1104093002

Cr-Commit-Position: refs/heads/master@{#327220}

components/bookmarks/browser/bookmark_model.cc

@@ -886,7 +886,7 @@ void BookmarkModel::RemoveNodeAndGetRemovedUrls(BookmarkNode* node,
   // This method does not explicitly acquires a lock.
   url_lock_.AssertAcquired();
   DCHECK(removed_urls);
-  BookmarkNode* parent = AsMutable(node->parent());
+  BookmarkNode* parent = node->parent();
   DCHECK(parent);
   parent->Remove(node);
   RemoveNode(node, removed_urls);