Change: Update dependencies, require Go >= 1.13

Restic now requires Go to be at least 1.13. This allows simplifications in the
build process and removing workarounds.

This is also probably the last version of restic still supporting mounting
repositories via fuse on macOS.

https://github.com/restic/restic/pull/2600
https://github.com/restic/restic/pull/2852
https://github.com/restic/restic/pull/2927