Revert "Only allow the system server to connect to sync adapters"

This reverts commit 4df2de8380.

There was a bug in the CL. Rather than fixing it forward, let's revert
it and fix it in a follow-up CL, so we'll only have to back-port
a single CL.

Bug: 203229608
Test: N/A, a follow-up CL will redo this change with a Test: line.

Change-Id: I5fddf283ace09996a2e5cfc272f8e9fd8168a114

core/java/android/content/AbstractThreadedSyncAdapter.java

@@ -21,7 +21,6 @@ import static com.android.internal.util.function.pooled.PooledLambda.obtainMessa
 import android.accounts.Account;
 import android.annotation.MainThread;
 import android.annotation.NonNull;
-import android.os.Binder;
 import android.os.Build;
 import android.os.Bundle;
 import android.os.Handler;
@@ -172,17 +171,8 @@ public abstract class AbstractThreadedSyncAdapter {
     }
 
     private class ISyncAdapterImpl extends ISyncAdapter.Stub {
-        private void enforceCallerSystem() {
-            final long callingUid = Binder.getCallingUid();
-            if (callingUid != Process.SYSTEM_UID) {
-                android.util.EventLog.writeEvent(0x534e4554, "203229608", -1, "");
-                return;
-            }
-        }
-
         @Override
         public void onUnsyncableAccount(ISyncAdapterUnsyncableAccountCallback cb) {
-            enforceCallerSystem();
             Handler.getMain().sendMessage(obtainMessage(
                     AbstractThreadedSyncAdapter::handleOnUnsyncableAccount,
                     AbstractThreadedSyncAdapter.this, cb));
@@ -197,8 +187,6 @@ public abstract class AbstractThreadedSyncAdapter {
                 }
                 Log.d(TAG, "startSync() start " + authority + " " + account + " " + extras);
             }
-            enforceCallerSystem();
-
             try {
                 final SyncContext syncContextClient = new SyncContext(syncContext);
 
@@ -254,7 +242,6 @@ public abstract class AbstractThreadedSyncAdapter {
 
         @Override
         public void cancelSync(ISyncContext syncContext) {
-            enforceCallerSystem();
             try {
                 // synchronize to make sure that mSyncThreads doesn't change between when we
                 // check it and when we use it