MAGETWO-69004: 2.2 Upgrade Testing - composer conflict

 - remove duplicate requires in Magento_Captcha

Author: Robert He

app/code/Magento/Captcha/composer.json

@@ -7,10 +7,7 @@
         "magento/module-customer": "100.2.*",
         "magento/module-checkout": "100.2.*",
         "magento/module-backend": "100.2.*",
-        "magento/framework": "100.2.*",
-        "zendframework/zend-db": "~2.5.0",
-        "zendframework/zend-captcha": "~2.5.0",
-        "zendframework/zend-session": "~2.5.0"
+        "magento/framework": "100.2.*"
     },
     "type": "magento2-module",
     "version": "100.2.0-dev",