CURLOPT: drop redundant long casts

[vszakats]

Also:

• CURLOPT_HSTS_CTRL.md: sync macro definitions with curl/curl.h.
  Perhaps it'd be better to delete copies like this?
• keep existing casts within the documentation to make sure it applies
  to older curl versions as well.
• CURLOPT_IPRESOLVE.md: re-add a long cast to man page, for consistency
  with the above.

[bagder]

I left them in the docs previously just because they were needed previously and people with older libcurl installations may read the newer documentation...

[bagder]

Not saying we can't do this, but it needs a think.

[vszakats]

I left them in the docs previously just because they were needed previously and people with older libcurl installations may read the newer documentation...

Yes, it'd probably be a reasonable thing to keep in-doc code (and perhaps examples?) backwards compatible. Though it makes maintenance more involved. Existing docs did not look conclusive, so went ahead to see how it'd look without this in mind.

If we want to do it consistently, it'll need fixing the other way around.