android: needs file_key_storage implementation

[ksedgwic]

In version 503b7ed

error[E0432]: unresolved import `super::file_key_storage`
 --> src/storage/key_storage_impl.rs:3:12
  |
3 | use super::file_key_storage::FileKeyStorage;
  |            ^^^^^^^^^^^^^^^^ could not find `file_key_storage` in `super`
  |
note: found an item that was configured out
 --> src/storage/mod.rs:2:5
  |
2 | mod file_key_storage;
  |     ^^^^^^^^^^^^^^^^
note: the item is gated here
 --> src/storage/mod.rs:1:1
  |
1 | #[cfg(any(target_os = "linux", target_os = "macos"))]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^