Remove gitignore, not part of Arch packaging guidelines

The need for git ignore files is better served by a single parent
.gitignore in the directory above all one's AUR packages (whether this
is just a loose file or part of an `aurpublish` setup or whether
`pkgctl` is being used). Each AUR package having it's own missmatched
ignore rules that behave differently depending on developer preferences
is fairly disruptive because tooling doesn't behave the same between
packages.