Fix: Replace androidx legacy widget space with space

The legacy [androidx.legacy.widget.Space] can no longer be found in the
project or the libraries, via transitive dependencies or otherwise, and
thus it is being replaced with plain [Space].

------------------------------------------------------------------------

WordPress/src/main/res/layout/zs_activity_request_list_scene_empty.xml
:14: Error: Class referenced in the layout file, androidx.legacy.widget
.Space, was not found in the project or the
libraries [MissingClass]

------------------------------------------------------------------------

WordPress/src/main/res/layout/zs_activity_request_list_scene_empty.xml

@@ -11,7 +11,7 @@
         android:gravity="center"
         android:orientation="vertical">
 
-        <androidx.legacy.widget.Space
+        <Space
             android:layout_width="0dp"
             android:layout_height="0dp"
             android:layout_weight="1" />
@@ -43,7 +43,7 @@
             android:paddingBottom="10dp"
             android:text="@string/request_list_empty_start_conversation" />
 
-        <androidx.legacy.widget.Space
+        <Space
             android:layout_width="0dp"
             android:layout_height="0dp"
             android:layout_weight="1" />