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/types/capture.h b/include/types/capture.h
index cd8f2a7..a9ced25 100644
--- a/include/types/capture.h
+++ b/include/types/capture.h
@@ -34,7 +34,7 @@
     struct pool_head *pool;		/* pool of pre-allocated memory area of (len+1) bytes */
 };
 
-extern struct pool_head *pool2_capture;
+extern struct pool_head *pool_head_capture;
 
 #endif /* _TYPES_CAPTURE_H */