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/thread/Name.hxx

@@ -20,6 +20,8 @@
 #ifndef MPD_THREAD_NAME_HXX
 #define MPD_THREAD_NAME_HXX
 
+#include "config.h"
+
 #if defined(HAVE_PTHREAD_SETNAME_NP) && !defined(__NetBSD__)
 #  define HAVE_THREAD_NAME
 #  include <pthread.h>

src/thread/SafeSingleton.hxx

@@ -20,7 +20,6 @@
 #ifndef MPD_SAFE_SINGLETON_HXX
 #define MPD_SAFE_SINGLETON_HXX
 
-#include "check.h"
 #include "Mutex.hxx"
 
 /**

src/thread/Slack.hxx

@@ -20,6 +20,8 @@
 #ifndef MPD_THREAD_SLACK_HXX
 #define MPD_THREAD_SLACK_HXX
 
+#include "config.h"
+
 #ifdef HAVE_PRCTL
 #include <sys/prctl.h>
 #endif

src/thread/Thread.cxx

@@ -17,7 +17,6 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#include "config.h"
 #include "Thread.hxx"
 #include "system/Error.hxx"
 

src/thread/Thread.hxx

@@ -20,7 +20,6 @@
 #ifndef MPD_THREAD_HXX
 #define MPD_THREAD_HXX
 
-#include "check.h"
 #include "util/BindMethod.hxx"
 #include "util/Compiler.h"