Drop the removed association_scopes_entities blocks that abort the manager fixtures

## Goal

Restore the RBAC seed data that `install-dev.sh` loads, by dropping the `association_scopes_entities` blocks left behind in two manager fixtures.

## Background

BA-7796 removed the table from the ORM metadata, but `fixtures/manager/example-users.json` and `fixtures/manager/example-roles.json` still declare it as a top-level key. `populate_fixture` looks every top-level key up in `metadata.tables` and raises `DataTransformationFailed` when it is missing. It also commits one table per transaction, so the abort keeps every table before the key and loses every table after it.

Lost on a fresh install:

- `example-users.json`: virtual_entities, entity_memberships, scope_bindings
- `example-roles.json`: role_presets, role_permission_presets, virtual_entities, entity_memberships, scope_bindings

Observed consequences on a fresh dev install: creating a vfolder fails with `VFolder ... was created in no project`, and `mgr image rescan` fails with `No virtual entity for entities: container_registry:`. install-dev.sh still exits 0, so the breakage surfaces only as two ERROR lines in its output.

## Acceptance criteria

- Neither fixture declares `association_scopes_entities` any more.
- A fresh `install-dev.sh` loads every table in both files.
- VFolder creation and `mgr image rescan` work on a fresh dev install.

## Notes

- Nothing is lost by the deletion. The 10 entries in example-users.json are all (project, user) and are already present in `entity_memberships`; 22 of the 27 in example-roles.json likewise.
- The remaining 5 are user->keypair, which the new model cannot express: `virtual_entities.entity_id` is a uuid column while those carry an access key string, and no current code treats a keypair as an RBAC entity. Whether that is intended is for BA-7796 to say.
- Related but out of scope: `populate_fixture` returns rather than continues when a table's row list is empty, which would silently skip every table after it.

JIRA Issue: BA-7815

Start with fixtures/manager/example-users.json and fixtures/manager/example-roles.json, then inspect populate_fixture and metadata.tables to confirm why the stale top-level key aborts loading. Run install-dev.sh on a fresh development install and verify that all fixture tables load; done when vfolder creation and mgr image rescan succeed without fixture errors.

Written by the indexing model from the issue text.