SimpleSAML_Auth_LDAP: Clean up unnecessary code.

The search()-function contained some code that was unnecessary. This
patch removes that code and simplifies the function.

Thanks to Ryan Panning for fixing this!

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@2982 44740490-163a-0410-bde0-09ae8108e29a