Bug#984807: Add stdmusic to freeciv-sound-standard package

[Fabian Greffrath]

HI Markus,

Am 08.09.2021 11:50, schrieb Markus Koschany:
would rather drop freeciv-sound-standard completely

agreed! The sounds and music are an integral part of the game, they add 
a mere 2 MB to the installation and are easily missed as they are 
currently packaged.

Thanks!

 - Fabian