Do not explicitly link libfolks-internal.la into things

Do not explicitly link libfolks-internal.la into things

libfolks.la embeds a copy of libfolks-internal.la, so every public
(or internal) symbol in libfolks-internal.la is available in
libfolks.la, even if linked with -Wl,--no-copy-dt-needed-entries.

If libfolks-internal.la defines a GObject type, then linking two copies
of it is actively harmful, because they can't both be registered with the
type system.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=687161
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Philip Withnall <philip@tecnocode.co.uk>