ST_RemovePoint — Remove a point from a linestring.
geometry ST_RemovePoint(geometry linestring, integer offset
Removes a point from a LineString, given its index (0-based). Useful for turning a closed line (ring) into an open linestring.
This function supports 3d and will not drop the z-index.
Guarantees no lines are closed by removing the end point of closed lines (rings). Assumes geom is of type LINESTRING
UPDATE sometable SET geom = ST_RemovePoint(geom, ST_NPoints(geom) - 1) FROM sometable WHERE ST_IsClosed(geom);