Remove the unused GetSessionChannelIDs from the db package (closes #254)

Neither the server nor any test calls this method.

Model: opus-5-5

internal/db/queries.go

@@ -1056,23 +1056,6 @@ func (database *Database) GetChannelMemberIDs(
 	return scanInt64s(rows)
 }
 
-// GetSessionChannelIDs returns channel IDs for a session.
-func (database *Database) GetSessionChannelIDs(
-	ctx context.Context,
-	sessionID int64,
-) ([]int64, error) {
-	rows, err := database.conn.QueryContext(ctx,
-		`SELECT channel_id FROM channel_members
-		 WHERE session_id = ?`, sessionID)
-	if err != nil {
-		return nil, fmt.Errorf(
-			"get session channel ids: %w", err,
-		)
-	}
-
-	return scanInt64s(rows)
-}
-
 // InsertMessage stores a message and returns its DB ID.
 // toSessionID is the session a DM or INVITE is sent to and
 // toChannelID the channel a channel message is sent to;