tcp-handler: Remove #include <cap-ng.h>

This commit removes the conditional import of <cap-ng.h> in tcp-handler,
because there are no dependencies on the libcap-ng API in tcp-handler.c.

src/knot/server/tcp-handler.c

@@ -28,9 +28,6 @@
 #ifdef HAVE_SYS_UIO_H			// struct iovec (OpenBSD)
 #include <sys/uio.h>
 #endif // HAVE_SYS_UIO_H
-#ifdef HAVE_CAP_NG_H
-#include <cap-ng.h>
-#endif /* HAVE_CAP_NG_H */
 
 #include "dnssec/random.h"
 #include "knot/server/server.h"