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/src/stick_table.c b/src/stick_table.c
index bd0c828..40c9258 100644
--- a/src/stick_table.c
+++ b/src/stick_table.c
@@ -51,7 +51,7 @@
 void __stksess_free(struct stktable *t, struct stksess *ts)
 {
 	t->current--;
-	pool_free2(t->pool, (void *)ts - t->data_size);
+	pool_free(t->pool, (void *)ts - t->data_size);
 }
 
 /*
@@ -226,7 +226,7 @@
 			return NULL;
 	}
 
-	ts = pool_alloc2(t->pool);
+	ts = pool_alloc(t->pool);
 	if (ts) {
 		t->current++;
 		ts = (void *)ts + t->data_size;