REORG: include: move cfgparse.h to haproxy/cfgparse.h

There's no point splitting the file in two since only cfgparse uses the
types defined there. A few call places were updated and cleaned up. All
of them were in C files which register keywords.

There is nothing left in common/ now so this directory must not be used
anymore.
diff --git a/src/vars.c b/src/vars.c
index 53afe1a..d58e1a3 100644
--- a/src/vars.c
+++ b/src/vars.c
@@ -2,7 +2,7 @@
 
 #include <haproxy/arg.h>
 #include <haproxy/api.h>
-#include <common/cfgparse.h>
+#include <haproxy/cfgparse.h>
 #include <haproxy/check.h>
 #include <haproxy/global.h>
 #include <haproxy/http.h>