removed os_compat.h

Only include headers which are really needed.  os_compat.h aimed to
make MPD easily portable, but was never actually made portable.

src/path.c

@@ -21,10 +21,11 @@
 #include "conf.h"
 #include "utils.h"
 #include "playlist.h"
-#include "os_compat.h"
 
 #include <glib.h>
 
+#include <string.h>
+
 static char *fs_charset;
 
 char *fs_charset_to_utf8(char *dst, const char *str)