curl: make global truly global

The GlobalConfig only exists in a single instance and it has worked like
this since the dawn of time. It is about time we stop passing around
pointers to what was already essentially a global object and instead
just use a... global.

It simplifies things.

Closes #18213

src/tool_progress.h

@@ -31,8 +31,7 @@ int xferinfo_cb(void *clientp,
                 curl_off_t ultotal,
                 curl_off_t ulnow);
 
-bool progress_meter(struct GlobalConfig *global,
-                    CURLM *multi,
+bool progress_meter(CURLM *multi,
                     struct curltime *start,
                     bool final);
 void progress_finalize(struct per_transfer *per);