composer.json: Remove abandoned libs `clue/buzz-react`..

..and `react/http-client`. `clue/soap-react` requires
these libs still, but the 2.x branch which requires
`react/http` isn't compatible with PHP 5.6.

composer.json

@@ -17,7 +17,6 @@
         "php": ">=5.6.3",
         "ext-curl": "*",
         "clue/block-react": "^1",
-        "clue/buzz-react": "~2.7.0",
         "clue/connection-manager-extra": "^1.1",
         "clue/http-proxy-react": "^1",
         "clue/mq-react": "^1.1",
@@ -35,7 +34,6 @@
         "react/dns": "^1",
         "react/event-loop": "^1.1",
         "react/http": "^1",
-        "react/http-client": "^0.5",
         "react/promise": "^2",
         "react/promise-stream": "^1",
         "react/promise-timer": "^1.5",