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/log.h b/include/proto/log.h
index 95c1701..c92217c 100644
--- a/include/proto/log.h
+++ b/include/proto/log.h
@@ -34,8 +34,8 @@
 #include <types/proxy.h>
 #include <types/stream.h>
 
-extern struct pool_head *pool2_requri;
-extern struct pool_head *pool2_uniqueid;
+extern struct pool_head *pool_head_requri;
+extern struct pool_head *pool_head_uniqueid;
 
 extern char *log_format;
 extern char default_tcp_log_format[];