lib: remove bad set.opt_no_body assignments

This struct field MUST remain what the application set it to, so that
handle reuse and handle duplication work.

Instead, the request state bit 'no_body' is introduced for code flows
that need to change this in run-time.

Closes #9888

lib/imap.c

@@ -1568,7 +1568,7 @@ static CURLcode imap_perform(struct Curl_easy *data, bool *connected,
 
   DEBUGF(infof(data, "DO phase starts"));
 
-  if(data->set.opt_no_body) {
+  if(data->req.no_body) {
     /* Requested no body means no transfer */
     imap->transfer = PPTRANSFER_INFO;
   }