async: remove constraint on ocaml < 5.0.0 on examples

Author: hannesm

async/examples/dune

@@ -2,12 +2,10 @@
   (name    test_client)
   (modules test_client)
   (preprocess (pps ppx_jane))
-  (enabled_if (< %{ocaml_version} 5.0.0))
   (libraries async core core_unix.command_unix tls-async))
 
 (executable
   (name    test_server)
   (modules test_server)
   (preprocess (pps ppx_jane))
-  (enabled_if (< %{ocaml_version} 5.0.0))
   (libraries async core core_unix.command_unix tls-async))