Remove experimentalNetworkStubbing (#318)

```experimentalNetworkStubbing``` option was removed and made the default behavior from version 6.0.0.
Ref: https://docs.cypress.io/guides/references/changelog#6-0-0

Issue resolved:
#309

Signed-off-by: am1tb <amit.banerjee.jsr@gmail.com>
(cherry picked from commit e6a9517)

cypress.json

@@ -16,6 +16,5 @@
     "password": "admin",
     "ENDPOINT_WITH_PROXY": false,
     "MANAGED_SERVICE_ENDPOINT": false
-  },
-  "experimentalNetworkStubbing": true
+  }
 }