Examples no longer need go mod replace

[aschmahmann]

Prior approach Run examples with -mod=flag so we do not have to tidy the go mod files in the example every time we change them in the repo.

fixes #8514

Proposal is:

1. Keep the modules, but drop the replace directive
2. In CI before running the tests run go get ipfs@the-branch-we're testing

[marten-seemann]

We have the same problem in libp2p. Unfortunately, running examples with -mod=mod is not an option, as the go-check workflow checks that all go.mod files are tidied.

What I did was create a Git pre-commit hook that runs go mod tidy for all Go modules in the repository. It's not a perfect solution, as git hooks have to be installed on every remote, but it's better than having CI fail all the time.

[aschmahmann]

@marten-seemann WDYT about the current PRs approach? I switched away from the -mod=mod to just testing the examples with upgrades dependencies.