Move ash/system/screen_security to Internals>Media>ScreenCapture

Bug: None
Change-Id: Ib1a2649b85bf832c09c0d1c4f164c10e61a3a651
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2387640


Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805668}