Делаю по доке: Remove the non-surviving or problematic monitors. For example, if you have three monitors, mon.a, mon.b, and mon.c, where only mon.a will survive, follow the example below:
monmaptool {map-path} --rm {mon-id}
# for example,
monmaptool /tmp/monmap --rm b
monmaptool /tmp/monmap --rm c