designate: Drop support for designate costing money

designate: Drop support for designate costing money

Chainsaw 3 added the designate cost along with extra build cost and
materials, and used both to make fortresses expensive.  Unlike build
cost and materials, the cost to designate didn't pass the test of
time: it was set to zero in Empire 2.  Get rid of it.

sect-chr selector cost and struct dchrstr member d_cost have to stay,
because they're still used to configure whether a sector may be
designated by players (see commit 8d792e1).

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>