Remove damienc from CREDITS.

There are no contributions in the tree from this contributor; he only
submitted some "powerglove" fist sprites to the project a long time
ago which were replaced, and subsequently appear to have been stolen
from another project without permission. See comments on this file
on Doomworld:

http://www.doomworld.com/idgames/index.php?file=combos/leftover.zip
Remove Dan L'Ecuyer from CREDITS.

Dan L'Ecuyer was credited as the author of the previous GENMIDI
lump that used to be used in Freedoom. This was subsequently
removed as it was based on the original Doom GENMIDI. Some
discussion of this can be found here:

http://www.doomworld.com/vb/freedoom/41470-texture1-copyright/