Subcontribution description is not shown

[kewisch]

Describe the bug
On http://indico.dev1/event/1/contributions/2/subcontributions/3 , the subcontribution description is not shown.

To Reproduce
Steps to reproduce the behavior:

1. Create subcontribution with description
2. Open relevant URL as above

Expected behavior
Description is shown

Additional context
Seems this might be as easy as adding a call to render_description in indico/modules/events/contributions/templates/display/subcontribution_display.html .