MINOR: thread: remove MAX_THREADS limitation

This one is now causing difficulties during the development phase and
it's going to disappear anyway, let's get rid of it.
diff --git a/src/thread.c b/src/thread.c
index 88bd232..1a0f5f2 100644
--- a/src/thread.c
+++ b/src/thread.c
@@ -995,13 +995,6 @@
 {
 	char *ptr = NULL;
 
-	if (MAX_THREADS < 1 || MAX_THREADS > LONGBITS) {
-		ha_alert("MAX_THREADS value must be between 1 and %d inclusive; "
-		         "HAProxy was built with value %d, please fix it and rebuild.\n",
-			 LONGBITS, MAX_THREADS);
-		exit(1);
-	}
-
 	preload_libgcc_s();
 
 	thread_cpus_enabled_at_boot = thread_cpus_enabled();