How can I remove a property from an entity in Drupal 7 I have a custom entity that was create a long time ago.  Now we want to update the schema to remove a property (not a field) that was defined in the original schema.

I've reviewed the Drupal API for managing schema for custom entities and I don't see anything that allows me to remove the column during a hook_update_N function.

Am I missing something obvious here?
You're looking for db_drop_field(). Although it's called a "field" here, it's essentially the remove-a-column-from-the-DB-table function.

Example from filter_update_7005():

// Drop the roles field from the {filter_format} table.
db_drop_field('filter_format', 'roles');