Revert "Narrow declared type of document.body to HTMLBodyElement | HTMLFrameSetElement" (#683)

This reverts commit 1f7b275.

Author: sandersn

baselines/dom.generated.d.ts

@@ -4218,7 +4218,7 @@ interface Document extends Node, NonElementParentNode, DocumentOrShadowRoot, Par
     /**
      * Specifies the beginning and end of the document body.
      */
-    body: HTMLBodyElement | HTMLFrameSetElement;
+    body: HTMLElement;
     /**
      * Returns document's encoding.
      */

inputfiles/overridingTypes.json

@@ -618,8 +618,7 @@
                             "nullable": false
                         },
                         "body": {
-                            "nullable": false,
-                            "override-type": "HTMLBodyElement | HTMLFrameSetElement"
+                            "nullable": false
                        }
                     }
                 }