Upgrade @metamask/subscription-controller to version 6.0.0

A new major version of `@metamask/subscription-controller`, 6.0.0, is now available. This issue has been assigned to you and your team because you code-own this package in the `core` repo. If this package is present in this project, please prioritize upgrading it soon to unblock new features and bugfixes.

Search the project manifests and lockfiles for @metamask/subscription-controller, then inspect how the current dependency version is declared. Upgrade it to 6.0.0 if it is present and verify the mobile project’s dependency checks and tests pass.

Written by the indexing model from the issue text.