Add script to undo build file generation

[dkelmer]

This also adds a newline to all the BUILD files because EOF insists on adding one so this is helpful for the future.

Related to https://github.com/bazelbuild/codelabs/issues/13

[dkelmer]

@aiuto, is this sort of what you were thinking of?

[hicksjoseph]

Is there any reason we couldn't update this and merge it?