Fix inconsistent and incorrect Roboto Medium usage

chrome/android/java/res/layout/contextual_search_promo_view.xml

 <?xml version="1.0" encoding="utf-8"?>
 <!-- Copyright 2016 The Chromium Authors. All rights reserved.
      Use of this source code is governed by a BSD-style license that can be
      found in the LICENSE file. -->
 
 <RelativeLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:chrome="http://schemas.android.com/apk/res-auto"
     android:id="@+id/contextual_search_promo"
     android:layout_width="match_parent"
@@ skipping 21 matching lines @@
 
     <org.chromium.ui.widget.ButtonCompat
         android:id="@+id/contextual_search_allow_button"
         android:layout_below="@id/contextual_search_promo_text"
         android:layout_alignParentEnd="true"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_gravity="end"
         android:layout_marginTop="16dp"
         android:layout_marginEnd="16dp"
-        android:fontFamily="sans-serif-medium"
         android:paddingStart="8dp"
         android:paddingEnd="8dp"
         android:text="@string/contextual_search_allow_button"
         android:textAllCaps="true"
         android:textColor="#FFF"
         android:textSize="14sp"
         chrome:buttonColor="@color/light_active_color" />
 
     <Button
         android:id="@+id/contextual_search_no_thanks_button"
         android:layout_below="@id/contextual_search_promo_text"
         android:layout_toStartOf="@id/contextual_search_allow_button"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_gravity="end"
         android:layout_marginTop="16dp"
         android:layout_marginEnd="16dp"
-        android:fontFamily="sans-serif-medium"
         android:paddingStart="8dp"
         android:paddingEnd="8dp"
         android:text="@string/contextual_search_no_thanks_button"
         android:textAllCaps="true"
         android:textColor="@color/light_active_color"
         android:textSize="14sp"
         style="@style/ButtonCompatBorderless" />
 
     <View
         android:layout_below="@id/contextual_search_allow_button"
         android:layout_width="match_parent"
         android:layout_height="1px"
         android:layout_marginTop="16dp"
         android:background="@color/contextual_search_promo_border_color" />
 
 </RelativeLayout>