subs: Clean up misuse of wu() around mission bomb damage

subs: Clean up misuse of wu() around mission bomb damage

Don't use multiple calls of wu() to print a single line, because that
creates a separate bulletin for each part.  The read command normally
merges the bulletins, but if the bulletins are more than five seconds
apart (clock jumped somehow), we get a bulletin header in the middle
of a line.  Unlikely to happen, but it also messes up pln_damage()'s
line wrapping (see commit e002bf2).  Clean it up.

The wu() misuse was introduced in Empire 2.

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