Remove .delete_me files for deprecated client apps

We had to manually add these two empty files to deprecated client app
folders in /client_apps/* as an indicator to a Rails initializer that
these client apps are now obsolete and need to removed BEFORE the JS
rake task runs. Otherwise, the rake task would fail trying to build
those client apps unless the initializer removed the folders.

Problem is, without this patch, anytime somebody runs `rake
canvas:compile_assets` or the JS rake tasks, their git HEAD will be
dirty with the now-removed .delete_me files. This patch removes the
files from the git history.

Closes CNVS-17516

TEST PLAN
---- ----

  - run `bundle exec rake canvas:compile_assets`
    + verify it works
  - run `git status` and make sure it does not list files in
    `/client_apps/canvas_quiz_*/.delete_me/`
  - browse the client_apps folder (`ls client_apps/*`) and verify
    neither canvas_quiz_statistics nor canvas_quiz_inspector exist

Change-Id: I0ab23ff6200e2425e0b3e104b2cdfd08e6a11629
Reviewed-on: https://gerrit.instructure.com/45813
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Derek DeVries <ddevries@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>