refactor: remove gimme and run_with_go_ver script

[kruskall]

Motivation/summary

Now that we have a toolchain directive explicitly defined in go.mod we can drop gimme and the shell script to ensure we are running the correct go version

Checklist

• Update CHANGELOG.asciidoc
• Documentation has been updated

For functional changes, consider:

• Is it observable through the addition of either logging or metrics?
• Is its use being published in telemetry to enable product improvement?
• Have system tests been added to avoid regression?

How to test these changes

Related issues

[mergify]

This pull request does not have a backport label. Could you fix it @kruskall? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-7.17 is the label to automatically backport to the 7.17 branch.
• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit.

NOTE: backport-skip has been added to this pull request.

[axw]

❤️ thanks for the cleanup. I think we can get rid of a few more Makefile variables, otherwise LGTM