delete method
Removes the blob with sha256. Returns true if it existed. Manual
deletion ignores pins, whoever holds them.
Implementation
@override
Future<bool> delete(String sha256) async {
if (!_keyPattern.hasMatch(sha256)) return false;
final db = _required;
return _serialized(() async {
final deleted = await _meta.record(sha256).delete(db);
await _deleteIfExists(_blobFile(sha256));
return deleted != null;
});
}