Revert "Fix Model.create_table(fail_silently=True) if schema is used."
I took a different approach that should work the same.
 Thanks for taking care of it!

This commit introduces a regression by overwriting the `PostgresqlDatabase.get_tables()` default value for `schema`.

``` python
(Pdb) db
<playhouse.pool.PooledPostgresqlExtDatabase object at 0xb620964c>
(Pdb) db.get_tables(schema=None)
[]
(Pdb) db.get_tables()
[u'migration', u'users']
```

One of the affected projects is https://github.com/cam-stitt/arnold
Basically migrations no longer go down.

@dkorduban sorry to ask for a revert, please provide and update the tests if you really want to fix this issue.

@coleifer please try to encourage the presence of tests in contributions :cry: 
