openid: Replace openid.claimed_id with openid.local_id.

The openid.claimed_id attribute is already available as 'openid'.
Replace it with the openid.local_id attribute instead.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@2624 44740490-163a-0410-bde0-09ae8108e29a