Fix some dead back button handling.

app/src/main/java/org/thoughtcrime/securesms/logsubmit/SubmitDebugLogActivity.java

@@ -313,13 +313,6 @@ public class SubmitDebugLogActivity extends BaseActivity {
     return false;
   }
 
-  @Override
-  public void onBackPressed() {
-    if (!viewModel.onBackPressed()) {
-      super.onBackPressed();
-    }
-  }
-
   @Override
   protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
     super.onActivityResult(requestCode, resultCode, data);

app/src/main/java/org/thoughtcrime/securesms/logsubmit/SubmitDebugLogViewModel.java

@@ -172,10 +172,6 @@ public class SubmitDebugLogViewModel extends ViewModel {
     });
   }
 
-  boolean onBackPressed() {
-    return false;
-  }
-
   enum Mode {
     NORMAL, LOADING, SUBMITTING
   }

app/src/main/java/org/thoughtcrime/securesms/megaphone/ClientDeprecatedActivity.java

@@ -1,8 +1,8 @@
 package org.thoughtcrime.securesms.megaphone;
 
-import android.annotation.SuppressLint;
 import android.os.Bundle;
 
+import androidx.activity.OnBackPressedCallback;
 import androidx.core.view.WindowInsetsCompat;
 
 import com.google.android.material.dialog.MaterialAlertDialogBuilder;
@@ -31,6 +31,13 @@ public class ClientDeprecatedActivity extends PassphraseRequiredActivity {
 
     findViewById(R.id.client_deprecated_update_button).setOnClickListener(v -> onUpdateClicked());
     findViewById(R.id.client_deprecated_dont_update_button).setOnClickListener(v -> onDontUpdateClicked());
+
+    getOnBackPressedDispatcher().addCallback(this, new OnBackPressedCallback(true) {
+      @Override
+      public void handleOnBackPressed() {
+        // The user must explicitly choose to update or to dismiss this screen.
+      }
+    });
   }
 
   @Override
@@ -44,12 +51,6 @@ public class ClientDeprecatedActivity extends PassphraseRequiredActivity {
     theme.onResume(this);
   }
 
-  @SuppressLint("MissingSuperCall")
-  @Override
-  public void onBackPressed() {
-    // Disabled
-  }
-
   private void onUpdateClicked() {
     PlayStoreUtil.openPlayStoreOrOurApkDownloadPage(this);
   }