Bid won message get trigger multi times if native template has multi <a> tag

[wqi1972]

Describe the bug
If native template has multi click links, then message: "Prebid Native" will get fired multi times, and it ends up bidWon event get fired multi times.

To Reproduce
Suppose there is a native template having following html:

<a href="%%CLICK_URL_UNESC%%%%PATTERN:hb_native_linkurl%%" target="_blank" class="pb-click" pbAdId="%%PATTERN:hb_adid%%">%%PATTERN:hb_native_title%%</a>
<img src="%%PATTERN:hb_native_image%%" />
<a href="%%CLICK_URL_UNESC%%%%PATTERN:hb_native_linkurl%%" target="_blank" class="pb-click" pbAdId="%%PATTERN:hb_adid%%"><img src="%%PATTERN:hb_native_icon%%"></a>

both title and icon both are clickable.
With such html, the issue will happen.

Reason:
code fire native ad impression are:

  function loadImpTrackers(adElements) {
      for(var i = 0; i < adElements.length; i++){
          let adId = readAdIdFromSingleElement(adElements[i]);
          fireTracker(adId, 'impression');
      }
  }

      if (adElements.length > 0) {
        loadImpTrackers(adElements);
      }

So the impression tracker get triggered for each <a> with pb-click class.

Suggest solution:
change loadImpTrackers so it only fires impress tracker for first element.

[wqi1972]

Since improvements from prebid/Prebid.js#5149 is coming, this is no need anymore.