Make more use of RELKIND_HAS_STORAGE()

This is a patch to make use of RELKIND_HAS_STORAGE() where appropriate, 
instead of listing out the relkinds individually.  No behavior change is 
intended.

This was originally part of the patch from [0], but it seems worth 
moving forward independently.


[0]: 
https://www.postgresql.org/message-id/flat/dc35a398-37d0-75ce-07ea-1dd71d98f8ec%402ndquadrant.com

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services