Add a Canary-specific icon in VisualElementsManifest.xml

This will fix the tile in Win10 being always the full-colour version,
even for Canary.

Removes the now unused SecondaryTile.png. (I think it was for Metro mode in
Win8? I'm not sure... but it was already unused as of this CL.)

R=grt@chromium.org
BUG=637477

Review-Url: https://codereview.chromium.org/2253323002
Cr-Commit-Position: refs/heads/master@{#414529}
8 files changed