dev-manual, mega-manual: Updated the workspace directory structure image

Removed the "mis-spelling" indicators.

(From yocto-docs rev: 558362fa59be94a8ebd29fbdbd932ef88d411272)

Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>