Delete AutoConfigurationReproTests as testing for early init is covered by WebServerFactoryCustomizerBeanPostProcessorTests

[wilkinsona]

When AutoConfigurationReproTests was introduced, it was testing some code in EmbeddedServletContainerAutoConfiguration that registered a EmbeddedServletContainerCustomizerBeanPostProcessor bean if one had not already been defined. That post-processor has now become WebServerFactoryCustomizerBeanPostProcessor that's registered by ReactiveWebServerFactoryAutoConfiguration or ServletWebServerFactoryAutoConfiguration.

[wilkinsona]

In fact, we can delete the class entirely as the post-processor and the potential for it to trigger early initialization is covered by WebServerFactoryCustomizerBeanPostProcessorTests.