Bug 1501911 - Support 'address-level3' in @autocomplete for form fields. r=smaug

Form Autofill added support in bug 1481972. This change allows authors to feature detect our support.

dom/base/AutocompleteFieldList.h

@@ -60,7 +60,6 @@ AUTOCOMPLETE_UNSUPPORTED_FIELD_NAME(USERNAME, "username")
 AUTOCOMPLETE_UNSUPPORTED_FIELD_NAME(NEW_PASSWORD, "new-password")
 AUTOCOMPLETE_UNSUPPORTED_FIELD_NAME(CURRENT_PASSWORD, "current-password")
 AUTOCOMPLETE_UNSUPPORTED_FIELD_NAME(ADDRESS_LEVEL4, "address-level4")
-AUTOCOMPLETE_UNSUPPORTED_FIELD_NAME(ADDRESS_LEVEL3, "address-level3")
 AUTOCOMPLETE_UNSUPPORTED_FIELD_NAME(CC_GIVEN_NAME, "cc-given-name")
 AUTOCOMPLETE_UNSUPPORTED_FIELD_NAME(CC_ADDITIONAL_NAME, "cc-additional-name")
 AUTOCOMPLETE_UNSUPPORTED_FIELD_NAME(CC_FAMILY_NAME, "cc-family-name")

testing/web-platform/meta/html/semantics/forms/the-form-element/form-autocomplete.html.ini

@@ -70,9 +70,6 @@
   [address-level4 is an allowed autocomplete field name]
     expected: FAIL
 
-  [address-level3 is an allowed autocomplete field name]
-    expected: FAIL
-
   [transaction-currency is an allowed autocomplete field name]
     expected: FAIL