RFR: 8303410: Remove ContentSigner

[Sean Mullan]

On Tue, 28 Feb 2023 19:09:00 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

> The `-altsigner` and `-altsignerpath` options in JarSigner with the underlying `ContentSigner` mechanism were deprected in Java 9, for removal in Java 15. See [JDK-8076535](https://bugs.openjdk.org/browse/JDK-8076535), [JDK-8242260](https://bugs.openjdk.org/browse/JDK-8242260).
> 
> This PR suggests it's time to remove this code:
> 
> - The package `com/sun/jarsigner` is removed. This contained the `ContentSigner` and `ContentSignerParameters` along with a `package-info.java` file.
> - `JarSigner.java` is updated to remove processing of the `-altsigner` and `-altsignerpath` options and the loading and processing of the custom `ContentSigner`.
> - Similarly `c.s.s.t.jarsigner.Main` is updated to remove processing and mentioning of `-altsigner` and `-altsignerpath` options.
> - Mentions of the options in Resource files in the same directory is removed
> - The `jarsigner.1` man page is updated to remove the section on the deprecated options
> - The `Spec` and `Options` tests are update to remove usage of the `-altsigner` and `-altsignerpath` options.

I would add more words to the title of the issue to cover the changes, ex: "Remove ContentSigner APIs and jarsigner -altsigner and -altsignerpath options"

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PR: https://git.openjdk.org/jdk/pull/12791