Delete non-LRU cache in SPIRE Agent

[amoore877]

Pull Request check list

• Commit conforms to CONTRIBUTING.md?
• Proper tests/regressions included?
• Documentation updated?

Affected functionality
Remove the original caching implementation in SPIRE Agent, as well as size configuration.

Description of change
Per plan in #4224 , perform final update actions by making LRU Cache with size 1000 the default, non-configurable implementation.

Also per #4224 , not for release until at least 1.11 based on #5150 , which deprecates the options but does not delete them, goes out in 1.10.

Which issue this PR fixes
Fixes #4224

[amoore877]

It's always pleasing when a PR's deletions outnumber additions/modifications by 10:1 :)

[amoore877]

hmm couple CI failures need to look at, which run here but not locally

[azdagron]

Thanks for moving on this @amoore877. I think we need to hold of merging this until we open up the branch for 1.11.0 PRs. That's going to be ~3 months after we ship 1.10.0. Would you mind closing this PR until we get closer to that time?

[amoore877]

Thanks for moving on this @amoore877. I think we need to hold of merging this until we open up the branch for 1.11.0 PRs. That's going to be ~3 months after we ship 1.10.0. Would you mind closing this PR until we get closer to that time?

oh, I was prepared to just have this be open that long or longer and keep branch up-to-date :)

does something bad happen on keeping PR open?

[azdagron]

Heh, yeah, there are a few reasons we prefer to not have long-lived PRs that aren't making forward momentum:

1. It confuses project-wide metrics tracked by the CNCF around time-to-merge for PRs (helps track project velocity and health)
2. Bit of a nitpick, but we go through each PR in sync meetings and it gets a little old saying things like, "can't merge this one for a few more months" :)

[amoore877]

thanks for explaining :)