[Bug]: Redundant index oc_mounts.mounts_storage_index

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

create index mount_user_storage
    on nextclouddev.oc_mounts (storage_id, user_id);

create index mounts_storage_index
    on nextclouddev.oc_mounts (storage_id);

The duplicate index makes all INSERT and DELETE queries more expensive.
Should we have UPDATEs for storage_id, those are more expensive too.

Steps to reproduce

1. Install Nextcloud

Expected behavior

Efficient use of database indices

Installation method

None

Nextcloud Server version

28

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

No response

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

Start by locating the Nextcloud database schema or migration definitions for oc_mounts and the mount_user_storage and mounts_storage_index indexes. Compare the indexes created by a fresh installation, then verify that the redundant single-column index is removed without losing required lookup coverage.