Revert "MNG-6209 better executeMojo thread context classloader"

This reverts commit ec629f7d511eb910b4e80112a9fbe85ed8786f10.
diff --git a/maven-core/src/main/java/org/apache/maven/plugin/DefaultBuildPluginManager.java b/maven-core/src/main/java/org/apache/maven/plugin/DefaultBuildPluginManager.java
index 3af1125..b4f7a4d 100644
--- a/maven-core/src/main/java/org/apache/maven/plugin/DefaultBuildPluginManager.java
+++ b/maven-core/src/main/java/org/apache/maven/plugin/DefaultBuildPluginManager.java
@@ -106,11 +106,8 @@
             throw new PluginExecutionException( mojoExecution, project, e );
         }
 
-        // use project realm as thread context classloader to enable components from all extensions=true plugins
-        ClassRealm tccl = mojoExecution.getPlugin().isExtensions() ? project.getClassRealm() : pluginRealm;
-
         ClassLoader oldClassLoader = Thread.currentThread().getContextClassLoader();
-        Thread.currentThread().setContextClassLoader( tccl );
+        Thread.currentThread().setContextClassLoader( pluginRealm );
 
         MavenSession oldSession = legacySupport.getSession();