Social Links: Remove links to disconnected services

Props @obenland, ref 90419
Featured Content: Hide term based on term name rather than term id.

Since only the term name gets updated by the Customizer, the term_id
will not always be correct during preview. This might lead to confusion
when the previewed term is still visible, even though it is supposed to
be hidden.

Props @obenland, ref 90228
Correct CSS property.