Old migration base/0045_auto_20200507_0445 deletes maps bbox

[etj]

Snip of migrate --plan:

base.0044_resourcebase_bbox_polygon
    Add field bbox_polygon to resourcebase
layers.0028_auto_20200323_1945
    Raw Python operation
base.0045_auto_20200507_0445
    Remove field bbox_x0 from resourcebase
    Remove field bbox_x1 from resourcebase
    Remove field bbox_y0 from resourcebase
    Remove field bbox_y1 from resourcebase

layers.0028 is populating field bbox_polygon from fields bbox_x|y_0|1.
Only layers are handled, so the bbox for maps and other resources are lost forever.

This is a really old migration. We don't want to mess up with the dependency graph, so we may want to update all resources in one of the existing migrations.