Generate specific message for build flag declarations artifact

Many of the fields in `flag_artifact` are not valid in
the all_build_flag_definitions artifact.

Bug: 328495189
Test: manual
Ignore-AOSP-First: cherry-pick
Merged-In: I00eab1ef76f67f7db2118a6fc0d5771e3dd39fbb
Change-Id: I00eab1ef76f67f7db2118a6fc0d5771e3dd39fbb

cmd/release_config/build_flag_declarations/main.go

@@ -73,7 +73,7 @@ func main() {
 		(*flagArtifacts)[*fa.FlagDeclaration.Name] = fa
 	}
 
-	message := flagArtifacts.GenerateFlagArtifacts()
+	message := flagArtifacts.GenerateFlagDeclarationArtifacts()
 	err = rc_lib.WriteFormattedMessage(flags.output, flags.format, message)
 	if err != nil {
 		errorExit(err)