Revert^4 "Add TARGET_SYSTEM_PROP to system build.prop"

072c0e4fcb3f9952e0d0dda7d56a595bca55dfcb

Change-Id: I53a36f415a9bd472170f030f115039e623769acf
diff --git a/android/variable.go b/android/variable.go
index eb0e210..5356e85 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -506,6 +506,8 @@
 	OemProperties []string `json:",omitempty"`
 
 	ArtTargetIncludeDebugBuild *bool `json:",omitempty"`
+
+	SystemPropFiles []string `json:",omitempty"`
 }
 
 type PartitionQualifiedVariablesType struct {