debugcommands: drop base revision from debugindex Revlog index data consists of generic index metadata that will likely be implemented across all storage engines and revlog-specifc metadata. Most tests printing index data only care about the generic fields. This commit drops the printing of the base revision from `hg debugindex`. This value is an implementation detail of revlogs / delta chains. If tests are interested in verifying this implementation detail, `hg debugdeltachain` is a better command. Most tests were skipping over this field anyway. Tests that weren't looked like they were newer. So my guess is we forgot to make them skip the field to match the style of the older tests. This reinforces my belief that the base revision is not worth having in `hg debugindex`. Differential Revision: https://phab.mercurial-scm.org/D3027