Migrate all database tests from gopkg.in/check.v1 Suite-based testing
to standard Go tests with testify assert/require.
Changes:
- Remove empty Suite files (hscontrol/suite_test.go, hscontrol/mapper/suite_test.go)
- Convert hscontrol/db/suite_test.go to modern helpers only
- Convert 6 Suite test methods in node_test.go to standalone tests
- Convert 5 Suite test methods in api_key_test.go to standalone tests
- Fix stale global variable reference in db_test.go
The legacy TestListPeers Suite method was renamed to TestListPeersManyNodes
to avoid conflict with the existing modern TestListPeers function, as they
test different aspects (basic peer listing vs ID filtering).
424e26d636