Update BouncyCastle to version 1.69

Update BouncyCastle to version 1.69

The version 1.69 is chosen instead of 1.70, because the moxie build
would not download the jars, trying to download `...1.7.jar` instead.

Three class deprecations are fixed. `PEMWriter` and `X509Extension`
are replaced with their drop-in replacements `JcaPEMWriter` and
`Extension`. The `PasswordFinder` deprecation note says that "it is
no longer used". It also was never used in Gitblit's code, so it is
removed from the key par provider class.