Remove SecurityHeaders

We no longer need this since Spring Framework now provides
HttpHeaders.setBearerAuth

Issue: gh-5612

web/src/test/groovy/org/springframework/security/web/http/SecurityHeadersTests.java

@@ -1,42 +0,0 @@
-/*
- * Copyright 2002-2018 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.security.web.http;
-
-import org.junit.Test;
-
-import static org.assertj.core.api.Assertions.*;
-
-/**
- * @author Rob Winch
- * @since 5.1
- */
-public class SecurityHeadersTests {
-
-	@Test
-	public void bearerTokenWhenNullThenIllegalArgumentException() {
-		String bearerTokenValue = null;
-		assertThatThrownBy(() -> SecurityHeaders.bearerToken(bearerTokenValue))
-				.isInstanceOf(IllegalArgumentException.class);
-	}
-
-	@Test
-	public void bearerTokenWhenEmptyStringThenIllegalArgumentException() {
-		assertThatThrownBy(() -> SecurityHeaders.bearerToken(""))
-				.isInstanceOf(IllegalArgumentException.class);
-	}
-
-}