GitLab

This CL deprecates setWallpaper call in intent_helper.mojom.

It also removes set_wallpaper_delegate.h since it's no
longer needed.

This is going to be committed only after ag/1432663/ enters
canary.

Test=Manually test setting wallpaper with OGQ Backgrounds
  app in Arc++.

Bug=642465

Review-Url: https://codereview.chromium.org/2332063004
Cr-Commit-Position: refs/heads/master@{#419015}