test(logging): revert unnecessary slf4j-api dependencyManagement

Remove `slf4j-api` from `sdk-platform-java/java-showcase/pom.xml` dependency management, as the versions are already explicitly managed within the `gapic-showcase/pom.xml` profiles and base dependencies.

Author: westarle

sdk-platform-java/java-showcase/pom.xml

@@ -35,11 +35,6 @@
         <type>pom</type>
         <scope>import</scope>
       </dependency>
-      <dependency>
-        <groupId>org.slf4j</groupId>
-        <artifactId>slf4j-api</artifactId>
-        <version>2.0.16</version>
-      </dependency>
       <dependency>
         <groupId>com.google.api.grpc</groupId>
         <artifactId>proto-gapic-showcase-v1beta1</artifactId>