Update Maven Wrapper for generated projects to 3.9.6

Also removes 3.8 wrapper used for Boot versions < 3.1.0.

Closes gh-1523

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/build/maven/MavenProjectGenerationConfiguration.java

@@ -24,7 +24,6 @@
 import io.spring.initializr.generator.buildsystem.maven.MavenBuildSystem;
 import io.spring.initializr.generator.condition.ConditionalOnBuildSystem;
 import io.spring.initializr.generator.condition.ConditionalOnPackaging;
-import io.spring.initializr.generator.condition.ConditionalOnPlatformVersion;
 import io.spring.initializr.generator.io.IndentingWriterFactory;
 import io.spring.initializr.generator.packaging.war.WarPackaging;
 import io.spring.initializr.generator.project.ProjectGenerationConfiguration;
@@ -45,14 +44,7 @@
 public class MavenProjectGenerationConfiguration {
 
 	@Bean
-	@ConditionalOnPlatformVersion("[2.0.0.M1,3.1.0-RC1)")
-	public MavenWrapperContributor maven38WrapperContributor() {
-		return new MavenWrapperContributor("3.8");
-	}
-
-	@Bean
-	@ConditionalOnPlatformVersion("3.1.0-RC1")
-	public MavenWrapperContributor mavenWrapperContributor() {
+	MavenWrapperContributor mavenWrapperContributor() {
 		return new MavenWrapperContributor("3");
 	}