Disabled collaborator still receiving notifications on private repo

[tribly]

• Gitea version (or commit ref): 1.4.1-1
• Operating system: Arch Linux
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist:

Description

When you add a new collaborator to a private repository, he then sets it as watched, and you remove him as a collaborator afterwards, he still receives notifications for issues and is listed in the 'watching' list, but he himself is unable to unwatch it, since he can't access the repo anymore.

[lafriks]

Duplicate of #3782