removing them

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/df6a4d53180a8e4df3a369341466319be5fbc75b

commit df6a4d53180a8e4df3a369341466319be5fbc75b
Author: Sergio Villar Senin <svillar@igalia.com>
Date: Tue Jan 15 12:24:51 2019

Remove SigninManager's leftover includes from screen_locker.cc

Bug:  920205 
Change-Id: If2c256ac404e5235432755b31fa4d4d902117ef7
Reviewed-on: https://chromium-review.googlesource.com/c/1408908
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#622825}
[modify] https://crrev.com/df6a4d53180a8e4df3a369341466319be5fbc75b/chrome/browser/chromeos/login/lock/screen_locker.cc