removing doc that was copied by a mistake

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@1865 44740490-163a-0410-bde0-09ae8108e29a

modules/authtwitter/docs/authfacebook.txt

-Using the Facebook authenticatio source with simpleSAMLphp
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-Remember to configure `authsources.php`, with both API key and secret.
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-To get an API key and a secret, register the application at:
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- * <http://www.facebook.com/developers/>
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-Set the callback URL to be:
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- * `http://idp.example.org/simplesaml/module.php/authfacebook/linkback.php?next=`
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-Replace `idp.example.org` with your hostname.
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