Do not list curl and libcurl3. These are irrelevant.

This commits is a forward port of:
44d84353522b5a599b43cea6056e92e7726ae1a6
bf26aab24e0334cc2bfff9a4f834adbe4c99f5a2
c34ca50fe92e6d395f61eb7abb4917c8b910765a
Merge pull request #242 from owncloud/stable6-remove-curl

[stable6] Remove curl package from dependency list