bump updater API version to 3; deprecate firmware update command

Remove support for the HTC-specific "firmware" update command and the
corresponding edify function write_firmware_update().  This
functionality is now done by an edify extension library that lives in

Change-Id: I80858951ff10ed8dfff98aefb796bef009e05efb
diff --git a/updater/updater.h b/updater/updater.h
index 22fbfd2..bd60dc1 100644
--- a/updater/updater.h
+++ b/updater/updater.h
@@ -23,6 +23,7 @@
 typedef struct {
     FILE* cmd_pipe;
     ZipArchive* package_zip;
+    int version;
 } UpdaterInfo;