Revert "Prevent duplicate DynamicPropertyRegistry beans"

This partially reverts commit 4d4b189cce.
The changes to main code are no longer needed as Framework's test
context framework no longer defines a DynamicPropertyRegistry bean. The
changes to test code have been kept to verify that @SpringBootTest and
TestcontainersPropertySourceAutoConfiguration continue to work in
combination.

Closes gh-42275

spring-boot-project/spring-boot-testcontainers/src/main/java/org/springframework/boot/testcontainers/properties/TestcontainersPropertySourceAutoConfiguration.java

@@ -16,10 +16,6 @@
 
 package org.springframework.boot.testcontainers.properties;
 
-import org.springframework.beans.BeansException;
-import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
-import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
-import org.springframework.beans.factory.support.DefaultSingletonBeanRegistry;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.context.ConfigurableApplicationContext;
@@ -43,27 +39,9 @@ public class TestcontainersPropertySourceAutoConfiguration {
 	TestcontainersPropertySourceAutoConfiguration() {
 	}
 
-	@Bean
-	static RemoveTestDynamicPropertyRegistryBeanPostProcessor removeTestDynamicPropertyRegistryBeanPostProcessor() {
-		return new RemoveTestDynamicPropertyRegistryBeanPostProcessor();
-	}
-
 	@Bean
 	static DynamicPropertyRegistry dynamicPropertyRegistry(ConfigurableApplicationContext applicationContext) {
 		return TestcontainersPropertySource.attach(applicationContext);
 	}
 
-	static class RemoveTestDynamicPropertyRegistryBeanPostProcessor implements BeanFactoryPostProcessor {
-
-		@Override
-		public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
-			if (beanFactory instanceof DefaultSingletonBeanRegistry singletonBeanRegistry) {
-				singletonBeanRegistry
-					.destroySingleton("org.springframework.test.context.support.DynamicPropertiesContextCustomizer"
-							+ ".dynamicPropertyRegistry");
-			}
-		}
-
-	}
-
 }