Fix link failure on OS X

ndb/src/mgmsrv/Services.cpp:
  Remove explicit instantiation to fix link failure on OS X

ndb/src/mgmsrv/Services.cpp

@@ -1574,4 +1574,3 @@ MgmApiSession::report_event(Parser_t::Context &ctx,
 
 template class MutexVector<int>;
 template class Vector<ParserRow<MgmApiSession> const*>;
-template class Vector<BaseString>;