fix: Replace internal Structs class with google-cloud-core version (#1501)

* fix: Replace internal Structs class with google-cloud-core version

* fix: remove structsTest unit tests

* 🦉 Updates from OwlBot post-processor

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---------

Co-authored-by: cindy-peng <[email protected]>
Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: 3 people

google-cloud-logging/src/main/java/com/google/cloud/logging/Payload.java

@@ -18,6 +18,7 @@
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
+import com.google.cloud.Structs;
 import com.google.common.base.MoreObjects;
 import com.google.protobuf.Any;
 import com.google.protobuf.Struct;

google-cloud-logging/src/main/java/com/google/cloud/logging/Structs.java

@@ -77,7 +77,7 @@
       <dependency>
         <groupId>com.google.cloud</groupId>
         <artifactId>google-cloud-shared-dependencies</artifactId>
-        <version>3.20.0</version>
+        <version>3.21.0</version>
         <type>pom</type>
         <scope>import</scope>
       </dependency>