Remove @Deprecated from org.springframework.mock.jndi package

This commit removes the @Deprecated declaration on the
org.springframework.mock.jndi package, since such usage results in a
compiler warning on JDK 9+ which breaks Spring's JDK 9 and JDK 11 CI
builds.

https://bugs.openjdk.java.net/browse/JDK-6481080

See gh-22779

spring-test/src/main/java/org/springframework/mock/jndi/package-info.java

@@ -10,7 +10,6 @@
  * same JNDI names as within a Java EE container, both application code and
  * configuration can be reused without changes.
  */
-@Deprecated
 @NonNullApi
 @NonNullFields
 package org.springframework.mock.jndi;