Update notebooks for schema changes

[heather999]

As noted in recent GCRCatalogs releases: https://github.com/LSSTDESC/gcr-catalogs/releases/tag/v1.2.0rc1

in schema for dc2_dia_source, dc2_forced_source fields and dc2_source fields Ixx, Iyy, Ixy, IxxPSF, IyyPSF and IxyPSF have been renamed to Ixx_pixel, Iyy_pixel, etc. Units for the new fields are pixel^2 (had been incorrectly labeled asec2 in the old fields)

This impacts notebooks such as https://github.com/LSSTDESC/DC2-analysis/blob/master/validation/validate_dc2_run2.2i_object_table.ipynb which needs to be updated.