third_party/nixpkgs/flutter: accept dart dependencies
third_party/nixpkgs/flutter: accept dart dependencies

Tested in other commits. This change is isolated because it's backward
compatible, breaks nothing, and allows code outside of NixOS/nixpkgs to
provide custom dependencies to mkFlutter as they see fit.

google/note-maps,google/note-maps,google/note-maps,google/note-maps,google/note-maps,google/note-maps,google/note-maps,google/note-maps,google/note-maps,google/note-maps,google/note-maps