tools: remove disabling of already-disabled rule

`require-buffer` is only enabled in the `lib` directory. There is no
need to disable it in `test`.

PR-URL: #6013
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>

Author: Trott

test/.eslintrc

@@ -3,8 +3,6 @@
 rules:
   ## allow undeclared variables
   no-undef: 0
-  ## allow global Buffer usage
-  require-buffer: 0
   ## common module is mandatory in tests
   required-modules: [2, "common"]