
1. Open the Find window and select in Multiple Files. and then "Code Elements" from the drop-down menu in the upper part of the Find window.
2. To the right of Element it should be set to Is and to the right of that, from the very long drop-down menu, choose font (or type font, if you find the menu too long to choose from).

3. Then open up the part of the window called Change and at Element choose "Replace by its Content". That will remove every occurrence of the surrounding
... tag including all its attributes while preserving its contents like text and images.
4. Now in the bottom section make your selection according to whether you want to clean up entire sites or single files and add them to the list.

5. When all choices are done, before you hit the "Find all" button and have it all done, choose the fly-out menu in the window and Save search (call it something like stripfonttag) in the proposed location, so you can use these parameters again and again without having to rebuild them from scratch each time. The name of the search will appear in the fly-out menu from the search-window.
Then click Find all.
Important note: The author is not/may not be a natural English speaker and there is a high chance of mistakes in every way. Corrections and comments are welcome.