Revert^2 "Modify conditionals for BuildFromTextStub()"

This change modifies config.BuildFromTextStub() to return false when
deviceConfig.BuildFromSourceStub() is set to true.

This change resubmits https://r.android.com/2832580.

Test: m nothing
Bug: 311203379
Change-Id: I832364c3c42556e2b3aede2316e8927fd7163e91
diff --git a/android/variable.go b/android/variable.go
index 648e4cf..fe3a6d7 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -494,6 +494,8 @@
 	Release_expose_flagged_api *bool `json:",omitempty"`
 
 	BuildFlags map[string]string `json:",omitempty"`
+
+	BuildFromSourceStub *bool `json:",omitempty"`
 }
 
 type PartitionQualifiedVariablesType struct {