Relax parameter attribute check
We currently try to enforce that a user can't do:
```py
class MyModule(nn.Module):
def setup(self):
self.name1 = self.param('name2', ...)
```
But the check is brittle and entirely disallows assigning dicts
or lists of parameters. This check relaxes our heuristic such
that it doesn't run at all for lists or dicts of parameters
assigned to attributes during setup.
See https://github.com/google/flax/issues/705#issuecomment-738761853
for a bit more context.
