Remove sign-off requirement in contributing guidelines
Remove sign-off requirement in contributing guidelines

* Per latest Eclipse guidance

locationtech/geomesa,locationtech/geomesa,locationtech/geomesa,locationtech/geomesa,jrs53/geomesa,jrs53/geomesa,jrs53/geomesa,jrs53/geomesa,jrs53/geomesa,locationtech/geomesa,locationtech/geomesa,jrs53/geomesa