Fix PSS.requestStart() called for signed-in non-syncing user

SyncController used to create a SignInStateObserver that would call
ProfileSyncService.requestStart() on every sign-in. Soon users will be
able to be signed in but not syncing, so this CL removes the observer.
requestStart() is still called if sync is enabled, since
SignInManager.finishSignInAfterPolicyEnforced() still
calls AndroidSyncSettings.enableChromeSync() [1][2], eventually calling
SyncController.updateSyncStateFromAndroid().

[1] https://source.chromium.org/chromium/chromium/src/+/3073cfbd9528937c5cdf94a15c96f56206f1fac5:chrome/android/java/src/org/chromium/chrome/browser/signin/SigninManager.java;l=568
[2] https://source.chromium.org/chromium/chromium/src/+/3073cfbd9528937c5cdf94a15c96f56206f1fac5:chrome/android/java/src/org/chromium/chrome/browser/signin/SigninManager.java;l=805

Fixed: 1141512
Change-Id: I6cba35e710d768810c63592d969f3be753aa32e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490014
Commit-Queue: Victor Vianna <victorvianna@google.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820176}

chrome/android/java/src/org/chromium/chrome/browser/sync/SyncController.java

@@ -13,8 +13,6 @@ import org.chromium.base.Log;
 import org.chromium.base.ThreadUtils;
 import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.chrome.browser.profiles.Profile;
-import org.chromium.chrome.browser.signin.IdentityServicesProvider;
-import org.chromium.chrome.browser.signin.SigninManager;
 import org.chromium.chrome.browser.uid.UniqueIdentificationGenerator;
 import org.chromium.chrome.browser.uid.UniqueIdentificationGeneratorFactory;
 import org.chromium.components.sync.ModelType;
@@ -71,18 +69,6 @@ public class SyncController implements ProfileSyncService.SyncStateChangedListen
         mProfileSyncService.addSyncStateChangedListener(mSyncNotificationController);
 
         updateSyncStateFromAndroid();
-
-        IdentityServicesProvider.get()
-                .getSigninManager(Profile.getLastUsedRegularProfile())
-                .addSignInStateObserver(new SigninManager.SignInStateObserver() {
-                    @Override
-                    public void onSignedIn() {
-                        mProfileSyncService.requestStart();
-                    }
-
-                    @Override
-                    public void onSignedOut() {}
-                });
     }
 
     /**