Fetch: getAll() was removed from Headers (#5140)

See whatwg/fetch#506.

Author: annevk

fetch/api/headers/historical.any.js

@@ -0,0 +1,4 @@
+test(() => {
+  assert_false("getAll" in new Headers)
+  assert_false("getAll" in Headers.prototype)
+}, "Headers object no longer has a getAll() method")