Dropped stored role name/description and other superflous fields

For name and description, we'll derive these from the role_field and
content type, which is much better for lots of reasons (eg changing text
the future). Also ditched the rest of the fields comming from the
standard common base model, we didn't use them and they cost several
indexes on the table.

awx/main/models/credential.py

@@ -204,27 +204,19 @@ class Credential(PasswordFieldsModel, CommonModelNameNotUnique, ResourceMixin):
         help_text=_('Tenant identifier for this credential'),
     )
     owner_role = ImplicitRoleField(
-        role_name='Credential Owner',
-        role_description='Owner of the credential',
         parent_role=[
             'singleton:' + ROLE_SINGLETON_SYSTEM_ADMINISTRATOR,
         ],
     )
     auditor_role = ImplicitRoleField(
-        role_name='Credential Auditor',
-        role_description='Auditor of the credential',
         parent_role=[
             'singleton:' + ROLE_SINGLETON_SYSTEM_AUDITOR,
         ],
     )
     use_role = ImplicitRoleField(
-        role_name='Credential User',
-        role_description='May use this credential, but not read sensitive portions or modify it',
         parent_role=['owner_role']
     )
     read_role = ImplicitRoleField(
-        role_name='Credential REad',
-        role_description='May read this credential',
         parent_role=[
             'use_role', 'auditor_role', 'owner_role'
         ],