test: disallow unreachable code

PR-URL: https://github.com/nodejs/node/pull/2289
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Brendan Ashworth <brendan.ashworth@me.com>

test/.eslintrc

@@ -1,8 +1,6 @@
 ## Test-specific linter rules
 
 rules:
-  ## allow unreachable code
-  no-unreachable: 0
   ## allow undeclared variables
   no-undef: 0
   ## allow global Buffer usage