fix(browse): theme change with no state refresh

* cards.reset() is no longer needed
* onCleared is no longer needed：
  * It's called when the theme changes, and we didn't actually
want this, as we wanted to persist the rows in the ViewModel

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

@@ -156,9 +156,6 @@ open class CardBrowser :
 
     lateinit var viewModel: CardBrowserViewModel
 
-    /** List of cards in the browser.
-     * When the list is changed, the position member of its elements should get changed. */
-    private val cards get() = viewModel.cards
     private lateinit var deckSpinnerSelection: DeckSpinnerSelection
 
     @VisibleForTesting

AnkiDroid/src/main/java/com/ichi2/anki/browser/CardBrowserViewModel.kt

@@ -692,18 +692,6 @@ class CardBrowserViewModel(
 
     fun getRowAtPosition(position: Int) = cards[position]
 
-    override fun onCleared() {
-        super.onCleared()
-        invalidate()
-    }
-
-    private fun invalidate() {
-        Timber.d("invalidate")
-        // TODO: this may no longer be needed now we call invalidate from onCleared
-        cards.clear()
-        selectNone()
-    }
-
     private suspend fun updateSavedSearches(func: MutableMap<String, String>.() -> Unit): Map<String, String> {
         val filters = savedSearches().toMutableMap()
         func(filters)