fix logic in ap_method_list_(add|remove) in order:

       - to correctly reset bits
       - not to modify the 'method_mask' bitfield unnecessarily

Also remove a useless 'register' in the declaration of a variable.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1610813 13f79535-47bb-0310-9956-ffa450edef68