Refactor snmp_errors by removing a parameter which was always provided with NULL

[Girgias]

Refactoring snmp_error to remove useless docref param as it was always passed NULL

[nikic]

It looks like SNMP is currently not tested in CI, we need a --with-snmp build somewhere.

[Girgias]

It looks like SNMP is currently not tested in CI, we need a --with-snmp build somewhere.

Does seem like it as my first commit should have totally broke unit tests.
However, I'm worried that maybe some of the Error/Warning conditions aren't covered like the EXIF extension as seen on #4254

[nikic]

It looks like getting SNMP in CI is not easy. Just a --with-snmp build without running snmp server won't work.

[Girgias]

It looks like getting SNMP in CI is not easy. Just a --with-snmp build without running snmp server won't work.

That's kind of annoying, in theory, nothing should change but well that's the theory.

Should I just leave this until something can be figured out, as my knowledge of SNMP is pretty much non-existent?

[nikic]

Merged as 6bd66f7. I've verified locally that it builds, which is the best I can do for now.