migration: remove not used field xfer_limit

MigrationState->xfer_limit is only set to 0 in migrate_init().

Remove this unnecessary field.
Signed-off-by: NWei Yang <richardw.yang@linux.intel.com>
Message-Id: <20190326055726.10539-1-richardw.yang@linux.intel.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>

migration/migration.c

@@ -1681,7 +1681,6 @@ void migrate_init(MigrationState *s)
      * locks.
      */
     s->bytes_xfer = 0;
-    s->xfer_limit = 0;
     s->cleanup_bh = 0;
     s->to_dst_file = NULL;
     s->state = MIGRATION_STATUS_NONE;

migration/migration.h

@@ -117,7 +117,6 @@ struct MigrationState
 
     /*< public >*/
     size_t bytes_xfer;
-    size_t xfer_limit;
     QemuThread thread;
     QEMUBH *cleanup_bh;
     QEMUFile *to_dst_file;