Add deprecation warnings for the drupal.modules_enable property/target.

tasks/drupal.xml

@@ -229,11 +229,29 @@
             <param>${drupal.profile}</param>
         </drush>
 
+        <!-- @todo Remove this conditional in release 2.0 -->
+        <if>
+            <not><equals arg1="${drupal.modules_enable}" arg2="" /></not>
+            <then>
+                <echo level="warning" msg="The 'drupal.modules_enable' property has been deprecated; please update your build to manage per-environment configuration with the Config Split module instead (https://www.drupal.org/project/config_split)" />
+            </then>
+        </if>
+
         <!-- The public files directory, and everything in it, needs to be world writable. -->
         <exec command="chmod -R 777 ${drupal.settings.file_public_path.resolved}" checkreturn="true" />
     </target>
 
 
+    <!--
+        Target: drupal-enable-module
+
+        @todo Remove this target in release 2.0
+        -->
+    <target name="drupal-enable-module">
+        <echo level="warning" msg="The 'drupal-enable-module' target has been deprecated; please update your build to manage per-environment configuration with the Config Split module instead (https://www.drupal.org/project/config_split)" />
+    </target>
+
+
     <!--
         Target: drupal-dump-db