use preference to check remote verification state

This is more efficient than checking if the job is scheduled and avoids
showing it disabled if the user does something like manually cancelling
the job. The app knows how to restore the missing job, so it's not what
determines if this is enabled anymore.

app/src/main/java/app/attestation/auditor/AttestationActivity.java

@@ -435,10 +435,10 @@ public boolean onCreateOptionsMenu(final Menu menu) {
 
     @Override
     public boolean onPrepareOptionsMenu(final Menu menu) {
-        final boolean isRemoteVerifyScheduled = RemoteVerifyJob.isScheduled(this);
+        final boolean isRemoteVerifyEnabled = RemoteVerifyJob.isEnabled(this);
         menu.findItem(R.id.action_enable_remote_verify)
-                .setEnabled(isSupportedAuditee && !isRemoteVerifyScheduled);
-        menu.findItem(R.id.action_disable_remote_verify).setEnabled(isRemoteVerifyScheduled);
+                .setEnabled(isSupportedAuditee && !isRemoteVerifyEnabled);
+        menu.findItem(R.id.action_disable_remote_verify).setEnabled(isRemoteVerifyEnabled);
         menu.findItem(R.id.action_submit_sample).setEnabled(canSubmitSample &&
                 !SubmitSampleJob.isScheduled(this));
         return true;

app/src/main/java/app/attestation/auditor/RemoteVerifyJob.java

@@ -49,15 +49,16 @@ public class RemoteVerifyJob extends JobService {
 
     private RemoteVerifyTask task;
 
+    static boolean isEnabled(final Context context) {
+        return PreferenceManager.getDefaultSharedPreferences(context).contains(KEY_USER_ID);
+    }
+
     static boolean isScheduled(final Context context) {
         return context.getSystemService(JobScheduler.class).getPendingJob(PERIODIC_JOB_ID) != null;
     }
 
     static void restore(final Context context) {
-        if (!PreferenceManager.getDefaultSharedPreferences(context).contains(KEY_USER_ID)) {
-            return;
-        }
-        if (!isScheduled(context)) {
+        if (isEnabled(context) && !isScheduled(context)) {
             Log.d(TAG, "remote attestation is enabled but job was not scheduled, rescheduling it");
             try {
                 schedule(context, DEFAULT_INTERVAL);