GN: Remove Value::RecursivelySetOrigin.

This method has been unused for about four months:
  https://codereview.chromium.org/223783005/

It is probably worthwhile to remove it, since it's dead and untested.

Review URL: https://codereview.chromium.org/445393004

Cr-Original-Commit-Position: refs/heads/master@{#288744}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6ac690f3dc3624c2ab3c7cfda5d9948f13d85a86