check.h: remove obsolete header

Since we switched from autotools to Meson in commit
94592c1406, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

src/player/Thread.cxx

@@ -35,7 +35,6 @@
  * #MusicChunk instances around in #MusicPipe objects.
  */
 
-#include "config.h"
 #include "Control.hxx"
 #include "Outputs.hxx"
 #include "Listener.hxx"