Drop dependency management for Spring Plugin

Closes gh-18318

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -194,7 +194,6 @@
 		<spring-integration.version>5.2.0.RC1</spring-integration.version>
 		<spring-kafka.version>2.3.0.RC1</spring-kafka.version>
 		<spring-ldap.version>2.3.2.RELEASE</spring-ldap.version>
-		<spring-plugin.version>2.0.0.M1</spring-plugin.version>
 		<spring-restdocs.version>2.0.3.RELEASE</spring-restdocs.version>
 		<spring-retry.version>1.2.4.RELEASE</spring-retry.version>
 		<spring-security.version>5.2.0.RC1</spring-security.version>
@@ -3181,16 +3180,6 @@
 				<artifactId>spring-ldap-test</artifactId>
 				<version>${spring-ldap.version}</version>
 			</dependency>
-			<dependency>
-				<groupId>org.springframework.plugin</groupId>
-				<artifactId>spring-plugin-core</artifactId>
-				<version>${spring-plugin.version}</version>
-			</dependency>
-			<dependency>
-				<groupId>org.springframework.plugin</groupId>
-				<artifactId>spring-plugin-metadata</artifactId>
-				<version>${spring-plugin.version}</version>
-			</dependency>
 			<dependency>
 				<groupId>org.springframework.restdocs</groupId>
 				<artifactId>spring-restdocs-asciidoctor</artifactId>