spring-boot-server-tests is no longer testing the embedded servlet containers' static resource support

[wilkinsona]

1342e49 added spring-webmvc to the classpath of the test application. Unfortunately, this had the unintended side-effect of causing Spring MVC's static resource support to be used rather than the embedded containers'. We need to remove spring-webmvc from the test application's classpath and find a different way to test the negative match for @ConditionalOnWarDeployment. It might be worth adding something that also check that Spring MVC hasn't been auto-configured so that we don't accidentally reintroduce the problem in the future.