Remove unused images from c/b/r/ntp4/.

Bug: None
Change-Id: I07e2bdf4d964da38ad7c13504a519300f5005155
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1654548
Commit-Queue: Dan Beam <dbeam@chromium.org>
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#668653}