Stop signing jars.

Implements #28584.

CERT

------BEGIN CERTIFICATE-----
-MIIDaTCCAlGgAwIBAgIELle0dTANBgkqhkiG9w0BAQsFADBlMQswCQYDVQQGEwJV
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-q7OXN2iiRIxiIJwoQw==
------END CERTIFICATE-----

build @ e639c697

-Subproject commit 08514a32afefbeef848b80f9a338ee840c282604
+Subproject commit e639c697e9e94c6dbb26e946e5247c20a62c0661