CLEANUP: pools: pools-t.h doesn't need to include thread-t.h

This is probably a leftover from an older version to access MAX_THREADS.
diff --git a/include/haproxy/pool-t.h b/include/haproxy/pool-t.h
index c33ffc7..111ae3a 100644
--- a/include/haproxy/pool-t.h
+++ b/include/haproxy/pool-t.h
@@ -24,7 +24,6 @@
 
 #include <haproxy/api-t.h>
 #include <haproxy/list-t.h>
-#include <haproxy/thread-t.h>
 
 #define MEM_F_SHARED	0x1
 #define MEM_F_EXACT	0x2