Remove port 22 from the set of allowed FTP ports.

The collision with SSH ports caused some possible concerns with being
able to enumerate internal hosts. Analysis shows that Internet hosts
supporting FTP over port 22 are a small fraction, and likely not
accessed over the web.

Bug: 767354
Change-Id: I8958b4cc818b34127fd739d2dea58f498fb073c0
Reviewed-on: https://chromium-review.googlesource.com/860753
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Christopher Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528461}