Remove _legacyUndefinedCheck from the core modules

Change-Id: I1ca93ec2b9f7bad4c9d6ad1d3789c1f4f12b7d82

polygerrit-ui/app/elements/core/gr-account-dropdown/gr-account-dropdown.js

@@ -21,7 +21,6 @@
 
   Polymer({
     is: 'gr-account-dropdown',
-    _legacyUndefinedCheck: true,
 
     properties: {
       account: Object,

polygerrit-ui/app/elements/core/gr-error-dialog/gr-error-dialog.js

@@ -19,7 +19,6 @@
 
   Polymer({
     is: 'gr-error-dialog',
-    _legacyUndefinedCheck: true,
 
     /**
      * Fired when the dismiss button is pressed.

polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.js

@@ -27,7 +27,6 @@
 
   Polymer({
     is: 'gr-error-manager',
-    _legacyUndefinedCheck: true,
 
     behaviors: [
       Gerrit.BaseUrlBehavior,

polygerrit-ui/app/elements/core/gr-key-binding-display/gr-key-binding-display.js

@@ -19,7 +19,6 @@
 
   Polymer({
     is: 'gr-key-binding-display',
-    _legacyUndefinedCheck: true,
 
     properties: {
       /** @type {Array<string>} */

polygerrit-ui/app/elements/core/gr-keyboard-shortcuts-dialog/gr-keyboard-shortcuts-dialog.js

@@ -21,7 +21,6 @@
 
   Polymer({
     is: 'gr-keyboard-shortcuts-dialog',
-    _legacyUndefinedCheck: true,
 
     /**
      * Fired when the user presses the close button.

polygerrit-ui/app/elements/core/gr-main-header/gr-main-header.js

@@ -71,7 +71,6 @@
 
   Polymer({
     is: 'gr-main-header',
-    _legacyUndefinedCheck: true,
 
     hostAttributes: {
       role: 'banner',

polygerrit-ui/app/elements/core/gr-reporting/gr-reporting.js

@@ -146,7 +146,6 @@
   // eslint-disable-next-line prefer-const
   let GrReporting = Polymer({
     is: 'gr-reporting',
-    _legacyUndefinedCheck: true,
 
     properties: {
       category: String,

polygerrit-ui/app/elements/core/gr-router/gr-router.js

@@ -209,7 +209,6 @@
 
   Polymer({
     is: 'gr-router',
-    _legacyUndefinedCheck: true,
 
     properties: {
       _app: {

polygerrit-ui/app/elements/core/gr-search-bar/gr-search-bar.js

@@ -104,7 +104,6 @@
 
   Polymer({
     is: 'gr-search-bar',
-    _legacyUndefinedCheck: true,
 
     /**
      * Fired when a search is committed

polygerrit-ui/app/elements/core/gr-smart-search/gr-smart-search.js

@@ -23,7 +23,6 @@
 
   Polymer({
     is: 'gr-smart-search',
-    _legacyUndefinedCheck: true,
 
     properties: {
       searchQuery: String,