remove unused IE hack

lib/scripts/pngbehavior.htc

-// this is an ugly fix to make Internet Explorer work with transparent
-// PNG images - do your self a favour and use a real browser!
-
-<public:component>
-<public:attach event="onpropertychange" onevent="propertyChanged()" />
-<script>
-
-var supported = /MSIE (5\.5)|[6789]/.test(navigator.userAgent) && navigator.platform == "Win32";
-var realSrc;
-var blankSrc = DOKU_BASE+"lib/images/blank.gif";
-
-if (supported) fixImage();
-
-function propertyChanged() {
-   if (!supported) return;
-
-   var pName = event.propertyName;
-   if (pName != "src") return;
-   // if not set to blank
-   if ( ! new RegExp(blankSrc).test(src))
-      fixImage();
-};
-
-function fixImage() {
-   // get src
-   var src = element.src;
-
-   // check for real change
-   if (src == realSrc) {
-      element.src = blankSrc;
-      return;
-   }
-
-   if ( ! new RegExp(blankSrc).test(src)) {
-      // backup old src
-      realSrc = src;
-   }
-
-   // test for png
-   if ( /\.png$/.test( realSrc.toLowerCase() ) ) {
-      // set blank image
-      element.src = blankSrc;
-      // set filter
-      element.runtimeStyle.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='" + src + "',sizingMethod='scale')";
-   }
-   else {
-      // remove filter
-      element.runtimeStyle.filter = "";
-   }
-}
-
-</script>
-</public:component>