Delete deprecated SecurityPrerequisite

Remove `SecurityPrerequisite` which was deprecated in 2.0.6.

See gh-14846

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/SecurityPrerequisite.java

@@ -1,29 +0,0 @@
-/*
- * Copyright 2012-2018 the original author or authors.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.springframework.boot.autoconfigure.security;
-
-/**
- * Marker interface for beans that need to be initialized before any security
- * configuration is evaluated.
- *
- * @author Dave Syer
- * @deprecated since 2.0.6 since security prerequisites are not supported in Spring Boot 2
- */
-@Deprecated
-public interface SecurityPrerequisite {
-
-}