Fix bomb for non-tactical cargo bomber

Fix bomb for non-tactical cargo bomber

The various bombing functions silently skipped planes not carrying
bombs.  This sanity check was wrong: it checked capabilities "tactical
or not cargo" instead of "tactical or bomber", and failed for
non-tactical cargo bombers.  No such planes exist in the stock game.
The broken check comes from Chainsaw; it replaced an equally wrong
"not cargo" check.

Because pln_sel() lets only suitable planes go on a bombing run, the
broken sanity check is unnecessary.  Drop it.