Cleanup HttpPipelineMessage and HttpClientOptions

[pakrym]

1. Remove IServiceProvider from client options and transport as we don't use it
2. Remove HttpMessageOptions as they are not used
3. Rename HttpPipelineMessage.Cancellation to CancellationToken for consistency

Breaking change

Before:

    class Policy : HttpPipelinePolicy
    {
        private async Task ProcessAsync(HttpPipelineMessage message, ReadOnlyMemory<HttpPipelinePolicy> pipeline)
        {
            await DoSomething(message.Cancellation);
        }
    }

After:

    class Policy : HttpPipelinePolicy
    {
        private async Task ProcessAsync(HttpPipelineMessage message, ReadOnlyMemory<HttpPipelinePolicy> pipeline)
        {
            await DoSomething(message.CancellationToken);
        }
    }

[tg-msft]

I left a couple of questions, but I think the cleaning looks good.