Remove deprecated Go code

[jjngx]

Proposed changes

This PR removes deprecated code.

References:

• staticcheck:

➜  kubernetes-ingress git:(test/staticcheck) ✗ staticcheck ./internal/certmanager/test_files/*.go
internal/certmanager/test_files/util.go:26:2: rand.Seed has been deprecated since Go 1.20 and an alternative has been available since Go 1.0: As of Go 1.20 there is no reason to call Seed with a random value. Programs that call Seed with a known value to get a specific sequence of results should use New(NewSource(seed)) to obtain a local random generator.  (SA1019)

• Go docs: ref

Checklist

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

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork