My understanding is that they're simply removing the rear-facing seats 1DF on the Dash 8-300s. The reason for this is to reduce the seat count from 50 to 48, which will allow them to add more RJs without violating the mainline pilot contract scope agreement.
That agreement allows for jets of 31-76 seats to total 75% of the mainline narrowbody fleet count (with some additional sub-limits within that amount.) It also states that turboprops seating 50+ count toward that limit, while turboprops seating fewer than 50 do not. By removing two seats from the 11 Dash 8-300s in the fleet, the company can add 11 more RJs.