CLEANUP: pools: rename all pool functions and pointers to remove this "2"

During the migration to the second version of the pools, the new
functions and pool pointers were all called "pool_something2()" and
"pool2_something". Now there's no more pool v1 code and it's a real
pain to still have to deal with this. Let's clean this up now by
removing the "2" everywhere, and by renaming the pool heads
"pool_head_something".
diff --git a/include/proto/hdr_idx.h b/include/proto/hdr_idx.h
index 0536444..f65b3c6 100644
--- a/include/proto/hdr_idx.h
+++ b/include/proto/hdr_idx.h
@@ -25,7 +25,7 @@
 #include <common/config.h>
 #include <types/hdr_idx.h>
 
-extern struct pool_head *pool2_hdr_idx;
+extern struct pool_head *pool_head_hdr_idx;
 
 /*
  * Initialize the list pointers.