Simplified polyline

What is the edit to simplify collinear segments of a polyline with many divisions to no divisions in line?

For this particular case - select Tools -> Polyline -> Delete Between two nodes.  
And later, select corner nodes between which other nodes should be removed (according the image - the fist and the last nodes of polylines).

 

Thanks, sand1024,

Delete between two nodes worked in two steps.

1. Cover the starting point (cyan) by dragging the second point (blue) over it.

2. Execute the command Delete between two nodes with the starting (blue) and ending (blue) vertices.

Oh, and for sure you could also delete each individual vertex of polyline using "Delete node" command for polyline