Removes several deprecated modules, including glue.LDBDWClient, glue.ligolw, glue.gpstime, iterutils, and glue.markup. Removes glue.ldbd and glue.segmentdb, as part of transferring them to dqsegdb client. Uses pyproject.toml for all metadata, simple version specification. Assorted minor changes. Milestone for glue 4.0.0: https://git.ligo.org/lscsoft/glue/-/milestones/4#tab-issues