remove translateZ hack

while it does improve repaint performance on *some* setups (OS X+Chrome+Low-DPI),
it seems to have no effect on most (OS X+FF, OS X+Chrome+High-DPI, Linux+Chrome),
and the opposite effect on others (Linux+FF).

IPython/html/static/base/less/page.less

@@ -79,12 +79,6 b' body {'
 }
 
 #site {
-    // avoid repaints on size with translateZ(0)
-    -webkit-transform: translateZ(0);
-    -moz-transform: translateZ(0);
-    -ms-transform: translateZ(0);
-    -o-transform: translateZ(0);
-    transform: translateZ(0);
     width: 100%;
     display: none;
     .border-box-sizing();

IPython/html/static/style/style.min.css

@@ -8454,11 +8454,6 b' body {'
   height: 28px;
 }
 #site {
-  -webkit-transform: translateZ(0);
-  -moz-transform: translateZ(0);
-  -ms-transform: translateZ(0);
-  -o-transform: translateZ(0);
-  transform: translateZ(0);
   width: 100%;
   display: none;
   box-sizing: border-box;