Remove pre-fetching for grant associations

When finding grants, we were loading associations for some general
convenience. However, we do not inspect the grants in detail for our
current use cases -- we supply very specific join/where conditions and
check for their existence as the implementation of the authorization
rules.

This preloading would be useful for building an administrative
interface, for example, but is unncessary now. The reason to remove it
is to avoid complexity and a performance problem introduced by fetching
the institution memberships: we were loading all of them for any matched
institution and doing an in-memory join on the object graph. In
production, that can be a giant list, consuming excessive time and
memory.

This problem can be solved by "adjusting the combine", applying
appropriate pieces of the filter conditions the association nodes, but
it is not worth doing now. We would be doing extra work and extra
queries to throw the data away.

lauth/app/repositories/grant_repo.rb

@@ -14,8 +14,7 @@ def for_collection_class(username:, client_ip:, collection_class:)
           .join(collections.name.dataset, uniqueIdentifier: grants[:coll], dlpsDeleted: "f")
           .where(collections[:dlpsClass] => collection_class)
 
-        rel = grants.class.new(ds)
-        rel.to_a
+        grants.class.new(ds).to_a
       end
 
       def for(username:, collection:, client_ip: nil)
@@ -25,8 +24,7 @@ def for(username:, collection:, client_ip: nil)
         ds = base_grants_for(username: username, network: smallest_network)
           .where(grants[:coll] => collection.uniqueIdentifier)
 
-        rel = grants.class.new(ds)
-        rel.combine(:user, institutions: {institution_memberships: :users}).to_a
+        grants.class.new(ds).to_a
       end
 
       private

lauth/spec/repositories/grant_repo_spec.rb

@@ -59,15 +59,6 @@
 
           expect(grants).to eq []
         end
-
-        # TODO: extract this
-        describe "grant association loading" do
-          subject(:found_grant) { repo.for(username: "lauth-allowed", collection: collection).first }
-
-          it "loads user" do
-            expect(found_grant.user.userid).to eq grant.user.userid
-          end
-        end
       end
 
       context "with a member of an authorized institution" do