Improve context popup rendering (#30824)
Before, lot of empty space when no labels or body:
<img width="281" alt="Screenshot 2024-05-02 at 13 51 29"
src="https://github.com/go-gitea/gitea/assets/115237/
8a980ccd-d53c-43a3-a059-
dc8c614621e1">
After, empty space collapsed:
<img width="306" alt="Screenshot 2024-05-02 at 13 51 16"
src="https://github.com/go-gitea/gitea/assets/115237/
8d9c154d-5de1-43d0-8536-
afd9194d99b3">
All `<p>` (unsuitable) and `<small>` (discouraged in favor of css) tags
are removed.