Import deprecation decorators from astropy

The deprecation decorators can be imported directly from `astropy`, and
importing them through `astroquery.utils.decorators` is deprecated. This
commit updates the only instance of importing the decorators through
`astroquery.utils`

Author: eerovaher

astroquery/cadc/core.py

@@ -18,7 +18,7 @@
 from ..query import BaseQuery
 from bs4 import BeautifulSoup
 from astropy.utils.exceptions import AstropyDeprecationWarning
-from astroquery.utils.decorators import deprecated
+from astropy.utils.decorators import deprecated
 from astropy import units as u
 from . import conf