tidy-up: miscellaneous

- drop stray duplicate empty lines in docs, scripts, test data, include,
  examples, tests.
- drop duplicate PP parenthesis.
- curl-functions.m4: move literals to the right side in if expressions,
  to match rest of the source code.
- FAQ.md: delete language designator from an URL.
- packages: apply clang-format (OS400, VMS).
- scripts/schemetable.c: apply clang-format.
- data320: delete duplicate empty line that doesn't change the outcome.
- spacecheck: extend to check for duplicate empty lines
  (with exceptions.)
- fix whitespace nits

Closes #19936

docs/examples/postit2-formadd.c

@@ -74,7 +74,6 @@ int main(int argc, char *argv[])
                  CURLFORM_COPYCONTENTS, "postit2-formadd.c",
                  CURLFORM_END);
 
-
     /* Fill in the submit field too, even if this is rarely needed */
     curl_formadd(&formpost,
                  &lastptr,