PHPBench removed from dev deps

The prefered way is to install PHPBench using the CLI application (PHAR).

Author: Spomky

composer.json

@@ -46,7 +46,6 @@
         "guzzlehttp/psr7": "^1.4",
         "php-http/httplug-bundle": "^1.7",
         "php-http/mock-client": "^1.0",
-        "phpbench/phpbench": "^1.0@dev",
         "phpunit/phpunit": "^6.0",
         "satooshi/php-coveralls": "^1.0",
         "symfony/browser-kit": "^3.3|^4.0",