[resources/facebook] Remove the code to fetch & store friends

Facebook in its API v2.0 removed the ability to retrieve user's friends
list. This effectively means that importing Facebook contacts into local
address book is not possible anymore. This change will be forced on all
apps starting April 2015 and there is no replacement, even planned;
there is already API v2.1 out with no hints.

Together with deprecating the Chat APIs (also due in April 2015) they
are clearly forcing everyone to use only their apps/website exclusively
for what are probably the most interesting tasks on Facebook.

The rest of the resource functionality stays in tact - we still get
events, notes, posts and notifications.

This concerns only the frameworks port. However now that I'm thinking
about it, the stable (kdepim4) version will stop working completely in
April 2015 because the libkfbapi in the kde4 version is making calls to
the API v1.0, so the server will simply start returning errors and no
data. I think libkfbapi /could/ be fixed by just doing "s/v1.0/v2.1" on
the request URL, but there are likely some other breaking changes,
especially in the permissions list and permission names, which are set
by the resource. So in order to fix it for people running stable, new
libkfbapi release will be needed together with new Facebook resource.

CCMAIL:kde-pim@kde.org