refactor(nav): remove duplicate string

```
back_pressed_once -> Press back again to exit
back_pressed_once_reviewer -> Press back again to return
```

Issue 14558

Author: david-allison

AnkiDroid/src/main/java/com/ichi2/anki/AbstractFlashcardViewer.kt

@@ -572,7 +572,7 @@ abstract class AbstractFlashcardViewer :
 
     override fun setupBackPressedCallbacks() {
         onBackPressedDispatcher.addCallback(this, defaultOnBackCallback)
-        onBackPressedDispatcher.addCallback(this, exitViaDoubleTapBackCallback(R.string.back_pressed_once_reviewer))
+        onBackPressedDispatcher.addCallback(this, exitViaDoubleTapBackCallback())
         super.setupBackPressedCallbacks()
     }
 

AnkiDroid/src/main/java/com/ichi2/anki/DeckPicker.kt

@@ -652,7 +652,7 @@ open class DeckPicker :
 
     override fun setupBackPressedCallbacks() {
         onBackPressedDispatcher.addCallback(this, exitAndSyncBackCallback)
-        onBackPressedDispatcher.addCallback(this, exitViaDoubleTapBackCallback(R.string.back_pressed_once))
+        onBackPressedDispatcher.addCallback(this, exitViaDoubleTapBackCallback())
         onBackPressedDispatcher.addCallback(this, closeFloatingActionBarBackPressCallback)
         super.setupBackPressedCallbacks()
     }

AnkiDroid/src/main/java/com/ichi2/anki/android/back/ExitViaDoubleTapBackBackPressCallback.kt

@@ -18,7 +18,6 @@ package com.ichi2.anki.android.back
 
 import android.content.SharedPreferences.OnSharedPreferenceChangeListener
 import androidx.activity.OnBackPressedCallback
-import androidx.annotation.StringRes
 import androidx.preference.PreferenceManager
 import com.google.android.material.snackbar.Snackbar
 import com.ichi2.anki.AnkiActivity
@@ -37,14 +36,12 @@ import timber.log.Timber
  * @see Prefs.exitViaDoubleTapBack
  */
 // TODO: Convert this to a class when context parameters are usable
-fun AnkiActivity.exitViaDoubleTapBackCallback(
-    @StringRes stringRes: Int,
-): OnBackPressedCallback =
+fun AnkiActivity.exitViaDoubleTapBackCallback(): OnBackPressedCallback =
     object : OnBackPressedCallback(enabled = Prefs.exitViaDoubleTapBack) {
         lateinit var strongListenerReference: OnSharedPreferenceChangeListener
 
         override fun handleOnBackPressed() {
-            showSnackbar(stringRes, Snackbar.LENGTH_SHORT)
+            showSnackbar(R.string.back_pressed_once, Snackbar.LENGTH_SHORT)
             this.isEnabled = false
             HandlerUtils.executeFunctionWithDelay(Consts.SHORT_TOAST_DURATION) {
                 this.isEnabled = true

AnkiDroid/src/main/res/values/02-strings.xml

@@ -257,7 +257,6 @@
     <string name="password_empty">Password is required</string>
 
     <string name="back_pressed_once">Press back again to exit</string>
-    <string name="back_pressed_once_reviewer">Press back again to return</string>
 
     <!-- %% is required to display % symbol. Reference: https://stackoverflow.com/a/16834358 -->
     <string name="percentage">%s%%</string>