Taken from
[StackExchange](https://graphicdesign.stackexchange.com/questions/147506/inkscape-to-convert-multiple-paths-into-one-single-path).

1. Select everything, and do Ungroup Shift+Ctrl+G 5 times to remove all those
   unnecessary nested groups.

2. Do Path > Stroke to Path to turn the horizontal stroke into a path.

3. Now you can do Path > Combine, or alternatively do Path > Union if you want
   to get rid of any overlaps.

4. Do File > Cleanup document

5. To export as optimised SVG, do File > Save as, then select "Optimised SVG"
   from the file type dropdown.

6. In the Optimsed SVG Output dialog set up the items you want to keep and which
   you want to remove. Here are my settings