Description of problem:
The Summary in the Module Stream details view has been empty since pulp2 times. It's not returned by pulp3 API, kept nil in Katello::ModuleStream, maybe it's time to remove it.

How reproducible:
always

Is this issue a regression from an earlier version:
It probably was in the ancient history of pulp2 -> 3 migration

Steps to Reproduce:
1. Sync some repo with streams (like module_stream2 from QE fixture repos)
2. Navigate to Content > Content Types > Module Streams
3. Click on some stream name > Details tab

Actual behavior:
Value for the Summary is missing (although present in repo metadata)

Expected behavior:
The entire line should be missing