Delete "store" service

[exalate-issue-sync]

places to look:

• "store" dir
• docs
• ocis runtime

[wkloucek]

Unblocked by #8419.

As of today, there is still code: https://github.com/owncloud/ocis/tree/a8cbc612ccb9cb4d910130220ad957d4ce7a8958/services/store

@micbar this code could actually be removed after a depreciation period?

[micbar]

@butonic we can remove it already.