Exclude duplicate javax.activation classes from web services starter

In 2.3.1, the JAX-B API now depends on javax.activation-api. This has
caused duplicate Activation classes to appear in the starter due to
dependencies on both javax.activation:activation:1.1 and on
javax.activation:javax.activation-api:1.2. This commit removes the
duplicate classes by excluding the former in favour of the latter.

See gh-14754

spring-boot-project/spring-boot-starters/spring-boot-starter-web-services/pom.xml

@@ -21,6 +21,12 @@
 		<dependency>
 			<groupId>com.sun.xml.messaging.saaj</groupId>
 			<artifactId>saaj-impl</artifactId>
+			<exclusions>
+				<exclusion>
+					<groupId>javax.activation</groupId>
+					<artifactId>activation</artifactId>
+				</exclusion>
+			</exclusions>
 		</dependency>
 		<dependency>
 			<groupId>javax.xml.ws</groupId>