Remove deprecated window.showModalDialog()

ManualTests/showModalDialog-returnValue.html

Index: ManualTests/showModalDialog-returnValue.html
diff --git a/ManualTests/showModalDialog-returnValue.html b/ManualTests/showModalDialog-returnValue.html
deleted file mode 100644
index fbc3ee360f8ab6d317ae6e848a34b1dd78ecc520..0000000000000000000000000000000000000000
--- a/ManualTests/showModalDialog-returnValue.html
+++ /dev/null
@@ -1,13 +0,0 @@
-This test makes sure we don't crash when storing the return value from showModalDialog.  Popup blocking needs to be disabled for this test to run.<br>
-<script>
-if (showModalDialog("data:text/html,<script>returnValue={value:'PASS'}; close()</"+"script>").value == "PASS")
-    document.write("<span style='color:green'>Test passed.<br>");
-else
-    document.write("<span style='color:red'>Test failed due to incorrect result.<br>");
-value = showModalDialog("data:text/html,<script>close()</"+"script>");
-if (!value)
-    document.write("<span style='color:green'>Test passed.<br>");
-else
-    document.write("<span style='color:red'>Test failed due to incorrect result.<br>");
-
-</script>