Remove the sign-in menu item on macOS.

chrome/app/nibs/MainMenu.xib

 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
 <document type="com.apple.InterfaceBuilder3.Cocoa.XIB" version="3.0" toolsVersion="5056" systemVersion="13F34" targetRuntime="MacOSX.Cocoa" propertyAccessControl="none">
     <dependencies>
         <deployment version="1090" defaultVersion="1060" identifier="macosx"/>
         <development version="5100" identifier="xcode"/>
         <plugIn identifier="com.apple.InterfaceBuilder.CocoaPlugin" version="5056"/>
     </dependencies>
     <objects>
         <customObject id="-2" userLabel="File's Owner" customClass="BrowserCrApplication"/>
         <customObject id="-1" userLabel="First Responder" customClass="FirstResponder"/>
@@ skipping 15 matching lines @@
                                     <action selector="orderFrontStandardAboutPanel:" target="483" id="644"/>
                                 </connections>
                             </menuItem>
                             <menuItem isSeparatorItem="YES" id="236"/>
                             <menuItem title="^IDS_PREFERENCES" keyEquivalent="," id="129">
                                 <connections>
                                     <action selector="showPreferences:" target="483" id="554"/>
                                 </connections>
                             </menuItem>
                             <menuItem isSeparatorItem="YES" id="492"/>
-                            <menuItem title="^IDS_SYNC_MENU_PRE_SYNCED_LABEL$IDS_PRODUCT_NAME" tag="40030" hidden="YES" enabled="NO" id="664">
-                                <modifierMask key="keyEquivalentModifierMask"/>
-                                <connections>
-                                    <action selector="commandDispatch:" target="-1" id="666"/>
-                                </connections>
-                            </menuItem>
                             <menuItem title="^IDS_CLEAR_BROWSING_DATA" tag="40013" id="491">
                                 <string key="keyEquivalent" base64-UTF8="YES">
 CA
 </string>
                                 <modifierMask key="keyEquivalentModifierMask" shift="YES" command="YES"/>
                                 <connections>
                                     <action selector="commandDispatch:" target="-1" id="624"/>
                                 </connections>
                             </menuItem>
                             <menuItem title="^IDS_IMPORT_SETTINGS_MENU_MAC" tag="40014" id="662">
@@ skipping 495 matching lines @@
         </customObject>
         <customObject id="483" customClass="AppController">
             <connections>
                 <outlet property="closeTabMenuItem_" destination="450" id="623"/>
                 <outlet property="closeWindowMenuItem_" destination="73" id="622"/>
                 <outlet property="helpMenu_" destination="106" id="667"/>
             </connections>
         </customObject>
     </objects>
 </document>