Revert "Enforce clearing renderers' paint invalidation state"

LayoutTests/fast/repaint/bugzilla-6278-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "repaintRects": [
         [304, 132, 2, 199],
         [254, 132, 52, 235],
         [10, 317, 242, 50],
         [10, 281, 292, 50],
         [10, 132, 292, 199],
         [10, 132, 292, 144],
         [10, 132, 242, 235],
         [10, 132, 242, 180],
+        [8, 333, 784, 36],
         [8, 333, 300, 36],
-        [8, 331, 300, 36]
+        [8, 333, 300, 36],
+        [8, 331, 300, 36],
+        [0, 341, 800, 36]
       ]
     }
   ]
 }