Remove android.widget.Toolbar shadow

Use app:elevation="0dp" instead of android:elevation on your toolbar.
If it is not work, put your toolbar inside of a AppBarLayout and set app:elevation="0dp":

<android.support.design.widget.AppBarLayout
            android:id="@+id/appBarLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:elevation="0dp">
            ...
</android.support.design.widget.AppBarLayout>