chore(java-datastore): modernize submodule pom.xml

Author: chingor13

java-datastore/datastore-v1-proto-client/pom.xml

@@ -89,7 +89,6 @@
       <artifactId>api-common</artifactId>
     </dependency>
 
-    <!-- Test dependencies. -->
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>