ash::ShellDelegate: elim PreInit

ShellDelegate::PreInit is now only used by
WindowTreeHostManagerStartupTest.Startup which can effectively be tested
by other means.

Bug: 705713
Change-Id: Ieaa394db7603ab14ccaa79059303aff4011af5d0
Reviewed-on: https://chromium-review.googlesource.com/1169432
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583850}
11 files changed