CLEANUP: stats/cli: stop using appctx->st2

Instead, let's have the state as an enum inside the context. It's much
cleaner and safer as we know nobody else touches it.
diff --git a/src/http_ana.c b/src/http_ana.c
index 1968f84..d2da628 100644
--- a/src/http_ana.c
+++ b/src/http_ana.c
@@ -3927,7 +3927,8 @@
 	struct htx *htx;
 	struct htx_sl *sl;
 
-	appctx->st1 = appctx->st2 = 0;
+	appctx->st1 = 0;
+	ctx->state = STAT_ST_INIT;
 	ctx->st_code = STAT_STATUS_INIT;
 	ctx->flags |= uri_auth->flags;
 	ctx->flags |= STAT_FMT_HTML; /* assume HTML mode by default */