Blender version 2.82a or above.
Look at the number of vertices in the image mesh1.png and mesh3.png.
mesh1.png
mesh3.png
To reduce the number of vertices as in mesh3.png from mesh1.png, follow these steps.
1. Add a plane, go to top view. Select plane and scale it up by pressing S then 4, then 'Enter" key.Change to edit mode, select all the vertices. At the top see the list of mesh options like View,Select,Add,Mesh Vertex, Edge, Face, UV.
Select "Mesh" -> "Clean Up"-> "Dissolve Geometry". In the pop up window at the left bottom corner, gradually reduce the Ratio value to get the number of vertices as in mesh2.png. Make sure the shape of the plane is not changed while adjusting the Ratio value. Now the vertices/edges should look as in mesh2.png.
mesh2.png
Next, in Edit mode, select edge select option. Select the edges which you want to remove then click on "Mesh"->"Delete"->"Dissolve Edges" to get a clean mesh as shown in image mesh3.png.
Save the file.
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