Remove blocking unbinds on in-fences

This code snippet shouldn't be needed but without it xe_exec_threads.rebind faults on TGL.

        /*
         * We can't do an unbind until all in syncs are signalled as we destroy
         * the PTEs immediately in the unbind code. If doing an async VM unbind,
         * no penalty for sleeping here.
         */
        if (VM_BIND_OP(args->op) == XE_VM_BIND_OP_UNMAP) {
                int i;

                for (i = 0; i < num_syncs; i++) {
                        err = xe_sync_entry_wait(&syncs[i]);
                        if (err)
                                return err;
                }
        }