Remove unused benchmarks

Would like to re-add benchmarks at some point, probably using PhpBench

Author: polyfractal

benchmarks/Elasticsearch/Benchmarks/AsyncVsSyncIndexingEvent.php

@@ -17,7 +17,6 @@
   "require-dev": {
     "phpunit/phpunit": "~4.7",
     "mockery/mockery": "0.9.4",
-    "athletic/athletic": "~0.1",
     "symfony/yaml": "2.4.3 as 2.4.2",
     "twig/twig": "1.*",
     "cpliakas/git-wrapper": "~1.0"