Rename product_services to system_ext

Bug: 134359158
Test: build and check if system_ext.img is created
Change-Id: I67f2e95dd29eac6a28e07e24ea973d3a134c3bfc
diff --git a/help.sh b/help.sh
index be07344..b02b14c 100755
--- a/help.sh
+++ b/help.sh
@@ -40,8 +40,8 @@
                             Stands for "Vendor, NO Dependencies"
     pnod                    Quickly rebuild the product image from built packages
                             Stands for "Product, NO Dependencies"
-    psnod                   Quickly rebuild the product_services image from built packages
-                            Stands for "ProductServices, NO Dependencies"
+    senod                   Quickly rebuild the system_ext image from built packages
+                            Stands for "SystemExt, NO Dependencies"
     onod                    Quickly rebuild the odm image from built packages
                             Stands for "ODM, NO Dependencies"