Don't sanitize theme tags while trying to search through them, as it is...

Don't sanitize theme tags while trying to search through them, as it is unnecessary. It is also very expensive -- 50% of the pageload for a search was spent sanitizing tags. see #20103.

git-svn-id: https://core.svn.wordpress.org/trunk@20026 1a063a9b-81f0-0310-95a4-ce76da25c4cd