Fix incorrect description of transaction modes in the docs. (#1104)

In fact, the default is always true regardless of whether spring-tx is on the classpath or not.

src/main/docs/guide/includes/transaction.adoc

@@ -1,7 +1,4 @@
-By default, if `org.springframework:spring-tx` is in the test classpath (e.g. transitively via
-`io.micronaut.configuration:micronaut-hibernate-jpa-spring`), when using `@MicronautTest`, each `@Test` method will be
-wrapped in a transaction that will be rolled back when the test finishes. This behaviour can be changed by using the
-`transactional` and `rollback` properties.
+When using `@MicronautTest` each `@Test` method will be wrapped in a transaction that will be rolled back when the test finishes. This behaviour can be changed by using the `transactional` and `rollback` properties.
 
 To avoid creating a transaction:
 
@@ -30,4 +27,4 @@ The following transaction modes are supported:
   in separate transactions.
 
 NOTE: Setup and cleanup methods are not wrapped in transactions in Kotest currently. As a result, transaction modes have
-no effect in Kotest.
+no effect in Kotest.