#370 is not fixed

[fbatschi]

Describe the bug
Unfortunately there is no way to reopen a issue, so i have to do a new one.

#370 seems not fixed to me. The commit 91a07ca is probably not working, since there is a ! to much in it.

Also, the warning Modify interactions needs either a either a source or features to work has a either a too much.

Affected version(s)

11.1.0

To Reproduce
Steps to reproduce the behavior:

1. Include a <ol-interaction-modify> in a without a `'features' key.

Expected behavior

• <ol-interaction-modify> without features works inside a <ol-source-vector>
• <ol-interaction-modify :features="foo"> works outside a <ol-source-vector>

without warnings.