Move Linux-specific LayoutTests to generic location

LayoutTests/fast/text/international/arabic-vertical-offset.html

 <style>
   /*  This font contains a line glyph(U+0606) and a square glyph(U+06E1), and
    *  has a 'mark' feature that locates the square glyph above the line glyph.
    *  This font was created by using FontForge from scratch.
    */
   @font-face {
     font-family: test;
     src: url(resources/font-for-arabic-offset-test.ttf);
   }
   div {
     font-family: test;
     font-size: 48pt;
   }
 </style>
 <p>The square glyph should be located above the line glyph.</p>
 <!-- Use arabic code points to make WebKit use ComplexTextController -->
 <div>&#x0606;&#x06e1;</div>
 <script>
 if (window.testRunner) {
     testRunner.waitUntilDone();
     setTimeout(function() { testRunner.notifyDone(); }, 100);
 }
 </script>