Deprecate from numpy import *

An idea for `numpy/__init__.py`:
```python
if sys.version_info[:2] >= (3, 7):
    __all__ += ['__don_t_do_this']

    def __getattr__(attr):
        if attr == '__don_t_do_this':
            warning.warn("Don't do this')
            return None
        raise AttributeError
```