Remove invalid comment/statement at role manager
Remove invalid comment/statement at role manager

An invalid comment and unecessary try except
statement are removed from role backend.

Since list_role_assignments_for_role is
implemented at assignment manager level and uses
list_role_assignments, which is currently
implemented by both sql and ldap backends, the
added comment is invalid and the related bug
is partially implemented.

Related-Bug: #1221805

Change-Id: I55a4df5aae4f21dc64738b0ddf53580d890b9d1c

rajalokan/keystone,dstanek/keystone,nuxeh/keystone,mahak/keystone,promptworks/keystone,nuxeh/keystone,vivekdhayaal/keystone,vivekdhayaal/keystone,roopali8/keystone,maestro-hybrid-cloud/keystone,vivekdhayaal/keystone,dstanek/keystone,himanshu-setia/keystone,jonnary/keystone,rushiagr/keystone,jamielennox/keystone,openstack/keystone,rajalokan/keystone,cernops/keystone,klmitch/keystone,takeshineshiro/keystone,ilay09/keystone,jonnary/keystone,openstack/keystone,jumpstarter-io/keystone,rajalokan/keystone,ajayaa/keystone,idjaw/keystone,ajayaa/keystone,himanshu-setia/keystone,rushiagr/keystone,ilay09/keystone,klmitch/keystone,promptworks/keystone,openstack/keystone,maestro-hybrid-cloud/keystone,jumpstarter-io/keystone,nuxeh/keystone,dims/keystone,mahak/keystone,dstanek/keystone,mahak/keystone,jamielennox/keystone,jumpstarter-io/keystone,rushiagr/keystone,takeshineshiro/keystone,idjaw/keystone,roopali8/keystone,dims/keystone,promptworks/keystone,cernops/keystone,ilay09/keystone