Remove unsupported from agent v3 install

[RRashmit]

Proposed changes

Removed the creation of the agent-dynamic.conf file and setting instance-groups
Remove FreeBSD specific commands

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[RRashmit]

Testing:

Verified it working with the modified scripts

[dhurley]

Can you also update https://github.com/nginx/agent/blob/907fd2c1c35b902391803eca4c28a505428dedc7/scripts/packages/postremove.sh by removing the freebsd references?

[dhurley]

I think you can remove the functions upgrade_config_file and add_default_config_file

[RRashmit]

I wonder if these are required for the default nginx-agent.conf case https://github.com/nginx/agent/pull/987/files#diff-d1856bfba76fc7d09934477bd66bb125a1e27e4e994b10ede89246b072ecefbaL12

[dhurley]

The default nginx-agent.conf is packaged with the agent so I actually dont know why these functions are here. Its probably for some legacy reasons. I'd say remove them and then test out the default install to make sure things still work.

[RRashmit]

Verified and looks good with the latest updates.