* swarm/storage/feed/lookup: Add context handling/forwarding
* swarm/storage/feed/lookup: Add test to catch bad hint
* swarm/storage/feed/lookup: Added context cancellation test
* swarm: clean up unused private types and functions
Those that were identified by code inspection tool.
* swarm/storage: move/add Proximity GoDoc from deleted private function
The mentioned proximity() private function was deleted in:
1ca8fc1e6fa0ab4ab1aaca06d6fb32e173cd5f2f