ReactiveOAuth2ClientAutoConfiguration Should Not Be Used in Servlet Environments

The [changes](https://github.com/spring-projects/spring-boot/commit/968a637e50a67c4aa2ab2ecf70519851b9cd79b7#diff-3b69b7975848ca01f7a2128276eec2d5) for #14350 mean that `ReactiveOAuth2ClientAutoConfiguration` is used in Servlet applications using `WebClient` and it should not be. The conditions on `ReactiveOAuth2ClientAutoConfiguration` should exclude Servlet environments.