Drop meetings.invites_sent #3017

Problem

meetings.invites_sent is a boolean, default false, added to track whether a meeting's invite batch had gone out. The last read and the last write were removed in 39bbbe52 (2020-12-02, "Ignore invites_sent column from now on"). That commit even documents the intent: "Before we remove it, this commit will help us to stop considering it…". Nothing has touched the column since, and unlike the #3007 case it was never even added to ignored_columns, so it still loads on every meeting query.

Proposed change

Two-step, as with #3007:

1. PR 1: add invites_sent to self.ignored_columns on Meeting, deploy, soak.
2. PR 2: safety_assured { remove_column :meetings, :invites_sent, :boolean, default: false }, plus regenerate schema.rb.

Acceptance

• After PR 1: meeting queries no longer name the column; suite passes.
• After PR 2: column gone from schema.rb; full suite passes.

Labels: refactoring, trivial