tidy-up: delete, comment or scope C macros reported unused

To reduce the number `-Wunused-macro` compiler warnings:
- delete unused macros.
- comment out unused macro that are part of a set.
- move macros into the scope they are used.

This may be useful to enable by default, but there are tricky cases that
I didn't manage to fix and paused the effort. E.g. internal features
checks in `openssl.c`. There is more, once those are fixed.

Closes #16279

lib/cookie.c

@@ -483,7 +483,9 @@ static bool invalid_octets(const char *p)
 #define CERR_COMMENT       11 /* a commented line */
 #define CERR_RANGE         12 /* expire range problem */
 #define CERR_FIELDS        13 /* incomplete netscape line */
+#ifdef USE_LIBPSL
 #define CERR_PSL           14 /* a public suffix */
+#endif
 #define CERR_LIVE_WINS     15
 
 /* The maximum length we accept a date string for the 'expire' keyword. The