Duplicate indexes present on PostgreSQL

*This issue was originally created by [**@Omar007**](https://github.com/Omar007) at .*

### Background information

- **Dendrite version or git SHA**: v0.13.7
- **SQLite3 or Postgres?**: Postgres, `postgres:15-alpine`
- **Running in Docker?**: Yes, `ghcr.io/matrix-org/dendrite-monolith:v0.13.7`

### Description

- **What** is the problem: duplicate indexes that are not needed exist in the dendrite database when deployed on PostgreSQL.
- **Who** is affected: as far as I can tell it affects everyone using PostgreSQL. I don't know if a similar problem exists for SQLite.
- **How** is this bug manifesting: it affects database performance negatively.
- **When** did this first appear: probably during a migration/update where the new/extra indexes where added. I don't know which/when.

### Steps to reproduce

- Have dendrite deployed on PostgreSQL
- Analyze the database (an easy way for this specific case would be to use something like pgHero)
- Find that certain indexes encompass others

Indexes in question:
| Table | Affected Columns | Index 1 | Index 2 |
| --- | --- | --- | --- |
| federationsender_queue_edus | json_nid | federationsender_queue_edus_nid_idx | federationsender_queue_edus_json_nid_idx |
| federationsender_queue_pdus | json_nid | federationsender_queue_pdus_json_nid_idx | federationsender_queue_pdus_pdus_json_nid_idx |
| federationsender_relay_servers | server_name | federationsender_relay_servers_server_name_idx | federationsender_relay_server_server_name_relay_server_name_key |
| keyserver_one_time_keys | user_id, device_id | keyserver_one_time_keys_idx | keyserver_one_time_keys_unique |
| syncapi_output_room_events | room_id | syncapi_output_room_events_room_id_idx | syncapi_output_room_events_recent_events_idx |
| syncapi_peeks | room_id | syncapi_peeks_room_id_idx | syncapi_peeks_room_id_user_id_device_id_key |
| syncapi_presence | user_id | syncapi_presence_user_id | presence_presences_unique |
| syncapi_receipts | room_id | syncapi_receipts_room_id | syncapi_receipts_unique |
| userapi_pushers | app_id, pushkey | userapi_pusher_app_id_pushkey_idx | userapi_pusher_app_id_pushkey_localpart_idx |