remove duplicate attributes from attributes/default.rb

We should be testing with the default attributes, not setting our own,
for the default scenario. These were mostly duplicates from the default
attributes file and none of them require any changes to the tests, so it
seems they were pretty useless.

Implements: blueprint object-storage-cleanup
Change-Id: I1fd8c9ae413f497820bdac7212ce35340f838ec5