It is not used anymore, snmp indecies are now ets tables and not processes.

The module mnesia_frag_old_hash utilized the broken erlang:hash/2 function
which has been deprecated for a long time. Since erlang:hash/2 is now removed
there is no point in having this module any more.

To separate concerns and reduce confusion, avoid implementing two
behaviours in a single module. Make a single start_link() helper in
mnesia_sup and remove the unused mnesia_sup:start() utility function.

* dgud/mnesia/ext-backend/PR-858/OTP-13058:
  mnesia_ext: Add basic backend extension tests
  mnesia_ext: reuse snmp field for ext updates
  mnesia_ext: Create table/data containers from mnesia monitor not temporary processes
  mnesia_ext: Implement ext copies index
  mnesia_ext: Load table ext
  mnesia_ext: Dumper and schema changes
  mnesia_ext: Refactor mnesia_schema.erl
  mnesia_ext: Ext support in fragmented tables
  mnesia_ext: Backup handling
  mnesia_ext: Create schema functionality
  mnesia_ext: Add ext copies and db_fold to low level api
  mnesia_ext: Refactor record_validation code
  mnesia_ext: Add create_external and increase protocol version to monitor
  mnesia_ext: Add ext copies to records
  mnesia_ext: Add supervisor and behaviour modules