Revert the feature of the <shadow> element as 'a function call' to the previous behavior.

LayoutTests/fast/dom/shadow/composed-shadow-tree-walker-shadow-reprojection-expected.txt

 Tests for Composed Shadow DOM Tree Traversal APIs. Can only run within DRT
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 Multiple shadow root without shadow element
 Composed Shadow Tree:
 #a
         #c
 
@@ skipping 81 matching lines @@
 #f
 #b
 #h
 Traverse in backward.
 #h
 #b
 #f
 #d
 #a
 
-shadow fallback element reprojection
+Ignore shadow fallback elements
 Composed Shadow Tree:
 #a
         #i
                 #k
                 #c
-                #e
+                #b
                 #f
                         #g
                 #h
                 #m
 
 Traverse in forward.
 #a
 #i
 #k
 #c
-#e
+#b
 #f
 #g
 #h
 #m
 Traverse in backward.
 #m
 #h
 #g
 #f
-#e
+#b
 #c
 #k
 #i
 #a
 
 with inactive insertion points
 Composed Shadow Tree:
 #a
         #s
                 #u
                 #f
                 #b
                         #c
                 #d
                         #e
                 #l
                 #m
                 #n
-                #q
-                #r
                 #w
 
 Traverse in forward.
 #a
 #s
 #u
 #f
 #b
 #c
 #d
 #e
 #l
 #m
 #n
-#q
-#r
 #w
 Traverse in backward.
 #w
-#r
-#q
 #n
 #m
 #l
 #e
 #d
 #c
 #b
 #f
 #u
 #s
 #a
 
 PASS successfullyParsed is true
 
 TEST COMPLETE