RFC: Retire BCC PMDA

[myllynen]

The BCC PMDA emerged and was added in late 2017 / early 2018 and back then it was a new way to collect custom kernel metrics with the eBPF technology that had emerged earlier. While BCC PMDA worked nicely to certain extent (compatibility with kernel internals would require almost constant attention), the BCC framework was succeeded by the more lightweight libbpf + CO-RE effort. The BPF PMDA was added a few years after BCC PMDA leveraging this more modern approach while still utilizing BCC PMDA's modular approach and configuration.

Since the two PMDAs are largely overlapping, switching from BCC PMDA to BPF PMDA should be relatively straightforward, and given that there's no active maintenance or development for the older BCC PMDA happening anymore I think it's best that we'll retire it.

At the code level this should be mostly fairly mechanical changes, remove the PMDA, the related QA, and the packaging parts. There are some bcc references in the pcpatop code but those are probably some fallbacks given the same file refers to bpf as well.

[natoscott]

The pcp-atop code is indeed a compatibility fallback from pmdabpf to pmdabcc metrics - I think we can safely drop that nowadays. I suggest we note this PMDA as deprecated in pcp-7.1.0 and drop it in the next convenient future release after that.

[kurik]

I have not found anything other than atop that depends on the BCC code. I am not sure how many people use this PMDA; however, in my experience, BCC itself is quite sensitive to kernel updates, which causes cascading issues for the PMDA. Therefore, I am +1 on deprecating and removing it.