fix(deps): set gson via java-shared-deps (#878)

Gson dependency version should be set by the java-shared-
dependencies BOM, so that the artifacts listed in the google-
cloud-bom have the same set of the dependencies.

Author: suztomo

google-cloud-logging/pom.xml

@@ -24,7 +24,6 @@
     <dependency>
       <groupId>com.google.code.gson</groupId>
       <artifactId>gson</artifactId>
-      <version>2.9.0</version>
     </dependency>
     <dependency>
       <groupId>io.grpc</groupId>