tls-async: remove ocaml upper bound

Author: hannesm

packages/tls-async/tls-async.0.16.0/opam

@@ -13,7 +13,7 @@ build: [
 ]
 
 depends: [
-  "ocaml" {>= "4.08.0" & < "5.0.0"}
+  "ocaml" {>= "4.08.0"}
   "dune" {>= "3.0"}
   "tls" {= version}
   "x509" {>= "0.14.0"}