Calendar gets renamed when shared to someone else

[LukasReschke]

This is on 11.0.3 RC1.

1. Share calendar personal to someone
2. URL is changed to https://example.com/remote.php/dav/calendars/lukas/personal_shared_by_lukas/

This _shared_by_lukas should not be there. It breaks existing clients that sync against personal.

cc @georgehrke
cc @oparoz Your issue.

[LukasReschke]

I guess we need to backport #4060 as the PR that introduced the bug has also been backported at #3722

[LukasReschke]

Backport at #4301, applied on the affected instance and it should work now.

[rullzer]

#4301 is merged.