Clean up NettyClientUtils#createNettySslContext

[dwhjames]

Inserting a JDK javax.net.ssl.SSLContext into Netty originated in commit

akka-grpc/runtime/src/main/scala/akka/grpc/internal/NettyClientUtils.scala

Lines 59 to 82 in aa05239

	/**
	* INTERNAL API
	*
	* Given a Java [[SSLContext]], create a Netty [[SslContext]] that can be used to build
	* a Netty HTTP/2 channel.
	*/
	@InternalApi
	private def nettyHttp2SslContext(javaSslContext: SSLContext): SslContext = {
	// FIXME: Create a JdkSslContext using a normal constructor. Need to work out sensible values for all args first.
	// In the meantime, use a Netty SslContextBuild to create a JdkSslContext, then use reflection to patch the
	// object's internal SSLContext. It's not pretty, but it gets something working for now.
	// Create a Netty JdkSslContext object with all the correct ciphers, protocol settings, etc initialized.
	val nettySslContext: JdkSslContext = GrpcSslContexts
	.configure(GrpcSslContexts.forClient, SslProvider.JDK)
	.build.asInstanceOf[JdkSslContext]
	// Patch the SSLContext value inside the JdkSslContext object
	val nettySslContextField: Field = classOf[JdkSslContext].getDeclaredField("sslContext")
	nettySslContextField.setAccessible(true)
	nettySslContextField.set(nettySslContext, javaSslContext)
	nettySslContext
	}

in PR #266

It was removed in PR #964
to address Issue #946

It was returned in PR #979
to address Issue #978

---

Original comment was

    // FIXME: Create a JdkSslContext using a normal constructor. Need to work out sensible values for all args first.
    // In the meantime, use a Netty SslContextBuild to create a JdkSslContext, then use reflection to patch the
    // object's internal SSLContext. It's not pretty, but it gets something working for now.

---

This commit addresses the original FIXME comment, and avoids using
deprecated constructors on io.grpc.netty.shaded.io.netty.handler.ssl.JdkSslContext

[raboof]

good find!