Remove debug code from WP_Automatic_Updater::send_email().

Merges [25891] to the 3.7 branch.

props markmcwilliams for initial patch.
fixes #25678.

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git-svn-id: http://core.svn.wordpress.org/branches/3.7@25804 1a063a9b-81f0-0310-95a4-ce76da25c4cd