Update swift, Xcode and Objective-C

[KevinRaney]

Reasons for making this change:

Update headers for clarity and remove .DS_Store files since they do not make sense in the context of a source control repo.

Links to documentation supporting these rule changes:

.DS_Store Files

[ealeksandrov]

It's already a part of macOS.gitignore, no need to add OS-specific stuff in language templates.

[wirecat]

Thank you for contributing, but we don't accept OS specific rules in template files unless they're added to the OS specific template in Global.

See macOS.gitignore for an example. 🙇