Don't expose upload_processes

That's actually not good practise.
Realized this when checking for multiple symbol definition in issue
mentioned below.

Regards https://github.com/profanity-im/profanity/issues/1314

src/ui/window_list.c

@@ -50,6 +50,7 @@
 #include "ui/window_list.h"
 #include "xmpp/xmpp.h"
 #include "xmpp/roster_list.h"
+#include "tools/http_upload.h"
 
 static GHashTable *windows;
 static int current;
@@ -519,15 +520,7 @@ wins_close_by_num(int i)
         ProfWin *window = wins_get_by_num(i);
         if (window) {
             // cancel upload proccesses of this window
-            GSList *upload_process = upload_processes;
-            while (upload_process) {
-                HTTPUpload *upload = upload_process->data;
-                if (upload->window == window) {
-                    upload->cancel = 1;
-                    break;
-                }
-                upload_process = g_slist_next(upload_process);
-            }
+            http_upload_cancel_processes(window);
 
             switch (window->type) {
             case WIN_CHAT: