HDFParser has `drop_variables` other parsers have `skip_variables`

[jsignell]

I think these represent the same concept, so probably best to align HDFParser to match the others. Could do it with a deprecation cycle since that's such a high-profile parser :)

[norlandrhagen]

Nice catch!

[TomNicholas]

Yes good plan. Our parser design means there is nothing to enforce compliance across 3rd-party parsers, but we should at least try to be compliant for the parsers we ship ourselves.