CURLOPT: drop redundant long casts

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.

Closes #17791

docs/examples/http3.c

@@ -38,8 +38,7 @@ int main(void)
     curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
 
     /* Use HTTP/3 but fallback to earlier HTTP if necessary */
-    curl_easy_setopt(curl, CURLOPT_HTTP_VERSION,
-                     (long)CURL_HTTP_VERSION_3);
+    curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_3);
 
     /* Perform the request, res gets the return code */
     res = curl_easy_perform(curl);