Remove --illegal-access=warn from toolchain configuration

As of Java 17, it is ignored. Our Toolchain-based builds use at least
Java 17 so specifying it no longer has any effect.

Closes gh-30122

buildSrc/src/main/java/org/springframework/boot/build/toolchain/ToolchainPlugin.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -74,7 +74,6 @@ public class ToolchainPlugin implements Plugin<Project> {
 
 	private void configureTestToolchain(Project project, ToolchainExtension toolchain) {
 		List<String> jvmArgs = new ArrayList<>();
-		jvmArgs.add("--illegal-access=warn");
 		jvmArgs.addAll(toolchain.getTestJvmArgs().getOrElse(Collections.emptyList()));
 		project.getTasks().withType(Test.class, (test) -> test.jvmArgs(jvmArgs));
 	}