Remove frame flattening support as Chromium has no intention of using it

LayoutTests/fast/frames/flattening/frameset-flattening-grid-expected.txt

Index: LayoutTests/fast/frames/flattening/frameset-flattening-grid-expected.txt
diff --git a/LayoutTests/fast/frames/flattening/frameset-flattening-grid-expected.txt b/LayoutTests/fast/frames/flattening/frameset-flattening-grid-expected.txt
deleted file mode 100644
index fe6d6648fd629416d53f5bedb1db557cfc06a825..0000000000000000000000000000000000000000
--- a/LayoutTests/fast/frames/flattening/frameset-flattening-grid-expected.txt
+++ /dev/null
@@ -1,52 +0,0 @@
-layer at (0,0) size 1200x800
-  RenderView at (0,0) size 785x585
-layer at (0,0) size 785x800
-  RenderBlock {HTML} at (0,0) size 785x800
-    RenderFrameSet {FRAMESET} at (0,0) size 1200x800
-      RenderFrame {FRAME} at (0,0) size 600x200
-        layer at (0,0) size 600x200
-          RenderView at (0,0) size 600x200
-        layer at (0,0) size 600x200
-          RenderBlock {HTML} at (0,0) size 600x200
-            RenderBody {BODY} at (8,8) size 584x176 [bgcolor=#008000]
-              RenderBlock {P} at (0,0) size 584x18
-                RenderText {#text} at (0,0) size 445x18
-                  text run at (0,0) width 445: "Test for frameset flattening. The flattening only works inside the DRT."
-              RenderBlock {P} at (0,34) size 584x18
-                RenderText {#text} at (0,0) size 529x18
-                  text run at (0,0) width 529: "This frame should be 300px wide, 200px tall and not be scrollable (have scrollbars)."
-        layer at (0,0) size 300x200
-          RenderBlock (positioned) {DIV} at (0,0) size 300x200
-      RenderFrame {FRAME} at (600,0) size 600x200
-        layer at (0,0) size 600x200
-          RenderView at (0,0) size 600x200
-        layer at (0,0) size 600x200
-          RenderBlock {HTML} at (0,0) size 600x200
-            RenderBody {BODY} at (8,8) size 584x176 [bgcolor=#FF0000]
-              RenderBlock {P} at (0,0) size 584x18
-                RenderText {#text} at (0,0) size 529x18
-                  text run at (0,0) width 529: "This frame should be 300px wide, 200px tall and not be scrollable (have scrollbars)."
-        layer at (0,0) size 300x50
-          RenderBlock (positioned) {DIV} at (0,0) size 300x50
-      RenderFrame {FRAME} at (0,200) size 600x600
-        layer at (0,0) size 600x600
-          RenderView at (0,0) size 600x600
-        layer at (0,0) size 600x600
-          RenderBlock {HTML} at (0,0) size 600x600
-            RenderBody {BODY} at (8,8) size 584x576 [bgcolor=#FFFF00]
-              RenderBlock {P} at (0,0) size 584x18
-                RenderText {#text} at (0,0) size 529x18
-                  text run at (0,0) width 529: "This frame should be 600px wide, 600px tall and not be scrollable (have scrollbars)."
-        layer at (0,0) size 600x600
-          RenderBlock (positioned) {DIV} at (0,0) size 600x600
-      RenderFrame {FRAME} at (600,200) size 600x600
-        layer at (0,0) size 600x600
-          RenderView at (0,0) size 600x600
-        layer at (0,0) size 600x600
-          RenderBlock {HTML} at (0,0) size 600x600
-            RenderBody {BODY} at (8,8) size 584x576 [bgcolor=#0000FF]
-              RenderBlock {P} at (0,0) size 584x18
-                RenderText {#text} at (0,0) size 529x18
-                  text run at (0,0) width 529: "This frame should be 600px wide, 600px tall and not be scrollable (have scrollbars)."
-        layer at (0,0) size 600x600
-          RenderBlock (positioned) {DIV} at (0,0) size 600x600