tcp: remove the looping on pcb count in tcp_destroy()

This was useful when TCP timers were not able to reliably stop. Note that
in_pcbinfo_destroy() called later asserts that V_tcbinfo.ipi_count is 0.

This reverts 806929d514, b54e08e11a.

sys/netinet/tcp_subr.c

@@ -58,7 +58,6 @@
 #include <sys/refcount.h>
 #include <sys/mbuf.h>
 #include <sys/priv.h>
-#include <sys/proc.h>
 #include <sys/sdt.h>
 #include <sys/socket.h>
 #include <sys/socketvar.h>
@@ -1593,24 +1592,10 @@ SYSINIT(tcp_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_THIRD, tcp_init, NULL);
 static void
 tcp_destroy(void *unused __unused)
 {
-	int n;
 #ifdef TCP_HHOOK
 	int error;
 #endif
 
-	/*
-	 * All our processes are gone, all our sockets should be cleaned
-	 * up, which means, we should be past the tcp_discardcb() calls.
-	 * Sleep to let all tcpcb timers really disappear and cleanup.
-	 */
-	for (;;) {
-		INP_INFO_WLOCK(&V_tcbinfo);
-		n = V_tcbinfo.ipi_count;
-		INP_INFO_WUNLOCK(&V_tcbinfo);
-		if (n == 0)
-			break;
-		pause("tcpdes", hz / 10);
-	}
 	tcp_hc_destroy();
 	syncache_destroy();
 	in_pcbinfo_destroy(&V_tcbinfo);