Revert^2 "Conditionally pass kernel version to build.prop"

This reverts commit 29fed1efe8.

Reason for revert: Fixed breakage with aosp/3200730, verified with ABTD

Change-Id: I207abd188636673250eb9a070be95db0b82f39e7

android/variable.go

@@ -509,6 +509,8 @@ type ProductVariables struct {
 	ArtTargetIncludeDebugBuild *bool `json:",omitempty"`
 
 	SystemPropFiles []string `json:",omitempty"`
+
+	EnableUffdGc *string `json:",omitempty"`
 }
 
 type PartitionQualifiedVariablesType struct {