In node edit mode put the mouse on the line between 2 points, right click, then delete span. This would leave you with the rectangle to pocket with no lines inside. You are left with several "line" vectors and you will need to rejoin these into 1 rectangle by selecting 2 lines (shift key and click) then right click "join / close vectors", I used "Move end points"
Sorry if this doesn't make sense but I'm no expert.
Let me know if you need any further info.

Tried to attach file, but I can't work that one out LOL