Remove references to non-required kde-mm libs.

Bug 303447 claims that libkcddb and libkcompactdisc are both not
actually used by kscd, and should be removed from CMakeLists.txt.

I've done what I can to prove the reporter wrong, including:

- Code review (looking for usage of headers from classes exported by
libkcddb and libkcompactdisc)
- Building kscd without CMake references to either lib.
- Running ldd on the resulting executable to verify the report that the
  libraries are not used by the binary.
- Actually *using* kscd (with an external CD player no less) after the
  aforementioned changes. The track list even shows up so CDDB data is
  being read from somewhere.

I'm convinced now. kscd does not directly require either libkcompactdisc
(Solid appears to be used instead) or libkcddb (MusicBrainz3 is used).
It is possible that those two libs are indirectly used but kscd doesn't
care at this point.

BUG:303447