Drop libbz2 dependency

Dynamic linking against libbz2 was problematic on some distributions.
We only needed it for pcre's CLI (which we don't use) and ffmpeg's mkv
decompression in case a user forced encoder to use it, because its usage
is discouraged by the standard.

See https://github.com/itgmania/itgmania/issues/217 for the related
discussion.

CMake/SetupFfmpeg.cmake

@@ -22,7 +22,7 @@ list(APPEND FFMPEG_CONFIGURE
             "--disable-programs"
             "--disable-swresample"
             "--disable-vaapi"
-            "--enable-bzlib"
+            "--disable-bzlib"
             "--enable-gpl"
             "--enable-pthreads"
             "--enable-static"