remove guard on riak_search_vnode:start_vnode/1

fixes start issue caused by https://github.com/basho/riak_core/commit/783bd60f332402142a78805af2cc918c33d27ef4
Merge pull request #140 from basho/jrw-vnode-start-fix

remove guard on riak_search_vnode:start_vnode/1