Revert "Updates .gitignore files."

This reverts commit c485095984fa675dfec1b4e749ab77bc1f8e7506.

Conflicts:
	.gitignore

Our root .gitignore file is not directly checked in;
instead one should `cp gitignore.SAMPLE .gitignore` after
cloning the repository.

This allows it to be customised locally. I'm not sure why
we don't use `.git/info/exclude` for local customizations
instead.

Review by @paulp @adriaanm