extract2.php: Clean up old code.

- The _portals are no longer used. Some of them still exist
  on meta.wikimedia.org but only with content like
  "This is no longer used" or "{{Historical}}" etc.
  extract2.php was still parsing these on every request and doing
  a pointless string search/replace.

- The text/plain header is broken, PHP outputs text/html instead
  because it somehow called header() with the value as second
  argument, which is an incorrect invokation.

- Secure.wikimedia.org should no longer be exposed.

- Whitespace, single quotes, commented out code.

Bug: 38167
Change-Id: Ib77f5312e7667ce2ebc074172a12ad3c5efb3a13
Merge "extract2.php: Clean up old code."