Replace hiddenapi-{public,private}-list.txt with a CSV file

`hiddenapi` is being refactored to work with a single CSV file as
opposued to a multitude of text files (one per flag). This patch
changes the singleton rule for listing public/private APIs from
stubs to expect a CSV as an output.

Bug: 119068555
Test: compiles, hiddenapi-flags.csv unchanged
Change-Id: I622521d59979a6b01ecc8065a278412fedf7b9bc
diff --git a/android/variable.go b/android/variable.go
index 46b1155..8333635 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -273,7 +273,7 @@
 	EnforceSystemCertificateWhitelist []string `json:",omitempty"`
 
 	// TODO(ccross): move these to a Singleton in Soong
-	HiddenAPIPublicList        *string  `json:",omitempty"`
+	HiddenAPIStubFlags         *string  `json:",omitempty"`
 	HiddenAPIFlags             *string  `json:",omitempty"`
 	HiddenAPIExtraAppUsageJars []string `json:",omitempty"`
 }