O3: Remove assertion for case that is actually handled in code.

If an nonspeculative instruction has a fault it might not be in the
nonSpecInsts map.

src/cpu/o3/inst_queue_impl.hh

@@ -1199,7 +1199,7 @@ InstructionQueue<Impl>::doSquash(ThreadID tid)
                        !squashed_inst->isCompleted()) {
                 NonSpecMapIt ns_inst_it =
                     nonSpecInsts.find(squashed_inst->seqNum);
-                assert(ns_inst_it != nonSpecInsts.end());
+
                 if (ns_inst_it == nonSpecInsts.end()) {
                     assert(squashed_inst->getFault() != NoFault);
                 } else {