Drop react/datagram from require

We don't need it and it accidentally wasn't removed.

Author: WyriHaximus

composer.json

@@ -20,7 +20,6 @@
         "psr/container": "^1.0",
         "psr/log": "^1.1",
         "react-parallel/react-parallel": "^1.0",
-        "react/datagram": "^1.5",
         "rx/operator-extras": "^2.1",
         "thecodingmachine/safe": "^1.2",
         "wyrihaximus/constants": "^1.5",