remove duplicate img directory

docs/img/WIN-h100.png

docs/img/WIN-h150-long.png

docs/img/WIN.png

docs/img/YoTribe.jpg

docs/img/blog-wk2.png

docs/img/blog-wk3.jpeg

docs/img/blog-wk4.JPG

docs/img/btn-ambass.png

docs/img/btn-community.png

docs/img/btn-events.png

docs/img/btn-external.png

docs/img/btn-tools.png

docs/img/btn-win.png

docs/img/buttons.pptx

docs/img/call-notes-week5.gif

...img/call-notes-wk6-ProjectDevelopment-openSourceTools.png

docs/img/figures.key

docs/img/icon-at.png

docs/img/icon-dev-openWIN.key

docs/img/icon-doi.png