Delete TableKeyComparator assignment operator

The assignment operator of the `buf_` member is deleted. Deleting the
already private assignment operator of TableKeyComparator.

Bug: 339010060
Test: Presubmits
Change-Id: Ibd34e30485fd4cc3bca7eb7405a2f2efccfcdaf1
diff --git a/external/flatbuffers/include/flatbuffers/flatbuffers.h b/external/flatbuffers/include/flatbuffers/flatbuffers.h
index 0f45157..68f3ae1 100644
--- a/external/flatbuffers/include/flatbuffers/flatbuffers.h
+++ b/external/flatbuffers/include/flatbuffers/flatbuffers.h
@@ -1960,10 +1960,7 @@
     vector_downward &buf_;
 
    private:
-    TableKeyComparator &operator=(const TableKeyComparator &other) {
-      buf_ = other.buf_;
-      return *this;
-    }
+    FLATBUFFERS_DELETE_FUNC(TableKeyComparator &operator=(const TableKeyComparator &other))
   };
   /// @endcond