Remove unused file administrators.js

[hacodeorg]

Per this Slack discussion, pegasus/sites.v3/code.org/public/administrators.md.erb was deleted and replaced by administrators.erb, which no longer use apps/src/sites/code.org/pages/public/administrators.js.

The administrators.js file is no longer used in any file, causing staging and test builds to fail with this error

Running "lint-entry-points" task
✘ code.org/public/administrators ➜ ./src/sites/code.org/pages/public/administrators.js
  ✘ Entry points should only be used by one template but this one is used by 0!
[117 passed] [30 silenced] [1 failed]
Warning: 1 entry points do not conform to naming conventions.
Run grunt check-entry-points for details.
� Use --force to continue.

The fix is to remove administrators.js completely.