Revert "Use NewTabButton for new tab variation in GTS"

This reverts commit 315f9a8f.

Reason for revert: The new plus button doesn't work as expected. http://crbug.com/1042606

Original change's description:
> Use NewTabButton for new tab variation in GTS
> 
> Bug: 1042015
> Change-Id: Ic1ad4c0902725bc0a096b72f05f5fab92ef9d4d0
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2001265
> Auto-Submit: Yue Zhang <yuezhanggg@chromium.org>
> Reviewed-by: Theresa  <twellington@chromium.org>
> Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
> Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#731803}

TBR=twellington@chromium.org,wychen@chromium.org,yuezhanggg@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1042015
Change-Id: I7069b577daa0a0b5ab271e08b481599a422db253
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2003621Reviewed-by: Yue Zhang <yuezhanggg@chromium.org>
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#732494}

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

@@ -18,13 +18,15 @@
         android:background="?attr/selectableItemBackground"
         android:orientation="horizontal"
         android:visibility="gone">
-        <org.chromium.chrome.browser.toolbar.NewTabButton
-            style="@style/ToolbarButton"
-            android:layout_width="wrap_content"
+        <ImageView
+            android:layout_width="@dimen/toolbar_button_width"
+            android:layout_height="56dp"
             android:layout_gravity="start|top"
+            android:scaleType="center"
             android:paddingStart="16dp"
             android:paddingEnd="16dp"
-            android:contentDescription="@string/accessibility_toolbar_btn_new_tab" />
+            app:srcCompat="@drawable/new_tab_icon"
+            android:contentDescription="@string/accessibility_toolbar_btn_new_tab"/>
         <TextView
             android:layout_width="wrap_content"
             android:layout_height="match_parent"