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

tests/http/clients/Makefile.am

@@ -45,6 +45,9 @@ AM_CPPFLAGS += -DCURL_NO_OLDIES
 if USE_CPPFLAG_CURL_STATICLIB
 AM_CPPFLAGS += -DCURL_STATICLIB
 endif
+if DOING_NATIVE_WINDOWS
+AM_CPPFLAGS += -DWIN32_LEAN_AND_MEAN
+endif
 
 # Prevent LIBS from being used for all link targets
 LIBS = $(BLANK_AT_MAKETIME)

tests/http/clients/ws-data.c

@@ -40,9 +40,6 @@
 #endif
 
 #ifdef _WIN32
-#ifndef WIN32_LEAN_AND_MEAN
-#define WIN32_LEAN_AND_MEAN
-#endif
 #include <windows.h>
 #else
 #include <sys/time.h>

tests/http/clients/ws-pingpong.c

@@ -34,9 +34,6 @@
 #include <string.h>
 
 #ifdef _WIN32
-#ifndef WIN32_LEAN_AND_MEAN
-#define WIN32_LEAN_AND_MEAN
-#endif
 #include <windows.h>
 #else
 #include <sys/time.h>