Revert optimizations in Spring Modulith dependency setup

The removal of the core dependency causes the BOM not being added as
that's contained in the dependency declaration. Manually adding the BOM
(build.boms().add(…)) adds the BOM segment but does not declare the
version property that's needed to resolve it properly.

See gh-1490

start-site/src/main/java/io/spring/start/site/extension/dependency/springmodulith/SpringModulithBuildCustomizer.java

@@ -51,10 +51,7 @@ public void customize(Build build) {
 			dependencies.add("modulith-observability",
 					modulithDependency("observability").scope(DependencyScope.RUNTIME));
 		}
-		boolean persistenceBackendAdded = addEventPublicationRegistryBackend(build);
-		if (persistenceBackendAdded) {
-			dependencies.remove("modulith");
-		}
+		addEventPublicationRegistryBackend(build);
 		dependencies.add("modulith-starter-test",
 				modulithDependency("starter-test").scope(DependencyScope.TEST_COMPILE));
 	}

start-site/src/test/java/io/spring/start/site/extension/dependency/springmodulith/SpringModulithBuildCustomizerTests.java

@@ -71,16 +71,7 @@ void presenceOfSpringDataModuleAddsModuleEventStarter(String store) {
 		build.dependencies().add("data-" + store);
 		this.customizer.customize(build);
 		assertThat(build.dependencies().ids()).contains("modulith-starter-" + store);
-		assertThat(build.dependencies().ids()).doesNotContain("modulith");
-	}
-
-	@ParameterizedTest
-	@ValueSource(strings = { "jdbc", "jpa", "mongodb" })
-	void presenceOfSpringDataModuleRemovesCoreStarter(String store) {
-		Build build = createBuild("modulith");
-		build.dependencies().add("data-" + store);
-		this.customizer.customize(build);
-		assertThat(build.dependencies().ids()).doesNotContain("modulith");
+		assertThat(build.dependencies().ids()).doesNotContain("modulith-starter-core");
 	}
 
 	private Build createBuild(String... dependencies) {