[cr140][Android] Delete Most Visited Tiles placeholder from NTP

Removed noMvPlaceholderStub arg from MostVisitedTilesMediator.ctor
Removed MostVisitedTilesMediator.updateTilePlaceholderVisibility

Chromium change:
https://source.chromium.org/chromium/chromium/src/+/d67f572a5aa967e71a3fa5cbe8fd434be9933eb5

	Delete Most Visited Tiles placeholder from NTP

	This CL removes the "mv_tiles_placeholder_stub" view as it never
	actually appears in the New Tab Page (NTP) UI.

	The placeholder's visibility is set to View.VISIBLE when no tiles are
	present. However, its parent, mv_tiles_container, is only visible if and
	only if there are tiles to display. Consequently, if no tiles are
	present, "mv_tiles_container"'s visibility is View.GONE, preventing its
	child, "mv_tiles_placeholder_stub", from ever being rendered on the NTP.

	This CL deletes all related placeholder logic from the view binder, view
	properties, mediator, XML, PNG files, and tests.

	Bug: 421436204
	Change-Id: Iab3a2288a97dcfa2e7c137d5b1d6e7521a07176e
	Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6771167

android/java/apk_for_test.flags

@@ -58,7 +58,6 @@
 -keep class org.chromium.chrome.browser.suggestions.tile.MostVisitedTilesMediator {
     *** mTileGroup;
     public <init>(...);
-    *** updateTilePlaceholderVisibility(...);
 }
 
 -keep class org.chromium.chrome.browser.suggestions.tile.BraveMostVisitedTilesMediator {

android/java/org/chromium/chrome/browser/suggestions/tile/BraveMostVisitedTilesMediator.java

@@ -6,7 +6,6 @@
 package org.chromium.chrome.browser.suggestions.tile;
 
 import android.content.res.Resources;
-import android.view.ViewStub;
 
 import androidx.annotation.Nullable;
 
@@ -21,7 +20,6 @@ public class BraveMostVisitedTilesMediator extends MostVisitedTilesMediator {
             Resources resources,
             UiConfig uiConfig,
             MostVisitedTilesLayout mvTilesLayout,
-            ViewStub noMvPlaceholderStub,
             TileRenderer renderer,
             PropertyModel propertyModel,
             boolean isTablet,
@@ -31,7 +29,6 @@ public class BraveMostVisitedTilesMediator extends MostVisitedTilesMediator {
                 resources,
                 uiConfig,
                 mvTilesLayout,
-                noMvPlaceholderStub,
                 renderer,
                 propertyModel,
                 isTablet,
@@ -39,10 +36,6 @@ public class BraveMostVisitedTilesMediator extends MostVisitedTilesMediator {
                 tileCountChangedRunnable);
     }
 
-    protected void updateTilePlaceholderVisibility() {
-        // This function is kept empty to avoid placeholder implementation
-    }
-
     @Override
     public void onTileDataChanged() {
         super.onTileDataChanged();