Fix shortcut tests and remove legacy shortcut code for the Default-user

Fix shortcut tests and remove legacy shortcut code for the Default-user
Quick Launch shortcut.

InstallShortcutTest.CreateAllShortcutsSystemLevel has been broken since http://crrev.com/164849 ...

The test expectations had not been adjusted in this CL as setup_unittests.exe
doesn't run on the waterfall yet (issue #153829) and the breakage had gone
unnoticed.

Expectations have now been adjusted such that we no longer expect a system-level
(Default-user) Quick Launch shortcut, but a per-user Quick Launch shortcut for
the admin running the install as the product code's logic has been doing for over
a year...

Also remove the code cleaning up the legacy Default-user Quick Launch shortcut as
this cleanup code has been running for 21 months now and leaving this shortcut
behind for a few users is a no-op (i.e. the Default-user shortcut will get copied
to new Windows profiles and Active Setup will kick in a few seconds later to try
to install the same shortcut which will already exist... the UX result will be
the same: a single Chrome Quick Launch shortcut will be installed).

BUG=329239, 153829

Review URL: https://codereview.chromium.org/432273005

Cr-Commit-Position: refs/heads/master@{#288393}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288393 0039d316-1c4b-4281-b951-d872f2087c98