Use Jan 1 2009 as timestamp in OTA update ZIPs.

This is a follow-up to 6c41036bcf where
I forgot to update a section of OTA update ZIP code.

Bug: 26864066

(cherry picked from commit f735851fa9)

Change-Id: I4f85ce170ac72d13a9c8636414927a295e350458

tools/signapk/src/com/android/signapk/SignApk.java

@@ -722,9 +722,6 @@ class SignApk {
 
                 int hash = getDigestAlgorithm(publicKey, minSdkVersion);
 
-                // Assume the certificate is valid for at least an hour.
-                long timestamp = publicKey.getNotBefore().getTime() + 3600L * 1000;
-
                 Manifest manifest = addDigestsToManifest(inputJar, hash);
                 copyFiles(manifest, inputJar, outputJar, timestamp, 0);
                 addOtacert(outputJar, publicKeyFile, timestamp, manifest, hash);