REORG: include: move vars.h to haproxy/vars{,-t}.h

A few includes (sessions.h, stream.h, api-t.h) were added for arguments
that were first declared in function prototypes.
diff --git a/src/vars.c b/src/vars.c
index f69dbbb..b9aea6a 100644
--- a/src/vars.c
+++ b/src/vars.c
@@ -6,14 +6,12 @@
 #include <haproxy/http_rules.h>
 #include <haproxy/list.h>
 #include <haproxy/sample.h>
-
-#include <types/vars.h>
+#include <haproxy/vars.h>
 
 #include <haproxy/arg.h>
 #include <proto/http_ana.h>
 #include <proto/stream.h>
 #include <proto/tcp_rules.h>
-#include <proto/vars.h>
 #include <proto/checks.h>
 
 /* This contains a pool of struct vars */