Rename product_services to system_ext

Bug: 134359158
Test: build and check if system_ext.img is created
Change-Id: I67f2e95dd29eac6a28e07e24ea973d3a134c3bfc
diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 0e84327..4598317 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -276,8 +276,8 @@
   _RO_PRODUCT_RESOLVE_PROPS = ["ro.product.brand", "ro.product.device",
                                "ro.product.manufacturer", "ro.product.model",
                                "ro.product.name"]
-  _RO_PRODUCT_PROPS_DEFAULT_SOURCE_ORDER = ["product", "product_services",
-                                            "odm", "vendor", "system"]
+  _RO_PRODUCT_PROPS_DEFAULT_SOURCE_ORDER = ["product", "odm", "vendor",
+                                            "system_ext", "system"]
 
   def __init__(self, info_dict, oem_dicts):
     """Initializes a BuildInfo instance with the given dicts.