Raise the Netty 5 minimum required Java version to Java 11.
Motivation:
Java 11 has been out for some time, and Netty 5 is still some ways out.
There are also many good features in Java 11 that we wish to use, such as VarHandles, var-keyword, and the module system.
There is no reason for Netty 5 to not require Java 11, since Netty 4.x will still be supported for the time being.
Modification:
Remove everything in the pom files related to Java versions older than Java 11.
Remove the animal-sniffer plug-in and rely on the `--release` compiler flag instead.
Remove docker files related to Java versions older than Java 11.
Remove the copied SCTP APIs -- we should test this commit independently on Windows.
Remove the OpenJdkSelfSignedCertGenerator.java file and just always use Bouncy Castle for generating self-signed certificates for testing.
Make netty-testsuite tests pass by including Bouncy Castle as a test dependency, so we're able to generate our self-signed certificate.
Result:
Java 11 is now the minimum required Java version.
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