Drop '2' from presubmit's chromedriver2_unittests.

chromedriver_unittests is a duplicate target that will eventually replace chromedriver2_unittests.
BUG=none
NOTRY=true

Review URL: https://codereview.chromium.org/119753011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242899 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242899