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

lib/config-os400.h

@@ -132,7 +132,6 @@
 /* Define if you have the `socket' function. */
 #define HAVE_SOCKET
 
-
 /* The following define is needed on OS400 to enable strcmpi(), stricmp() and
    strdup(). */
 #define __cplusplus__strings__