Clean up axis2-json dependencies

- Remove explicit dependency on okio. Instead just use whatever version
moshi depends on.
- Ensure all moshi artifacts use the same version.
diff --git a/modules/json/pom.xml b/modules/json/pom.xml
index 2868487..f402c87 100644
--- a/modules/json/pom.xml
+++ b/modules/json/pom.xml
@@ -42,6 +42,10 @@
         <tag>HEAD</tag>
     </scm>
 
+    <properties>
+        <moshi.version>1.13.0</moshi.version>
+    </properties>
+
     <dependencies>
         <dependency>
             <groupId>org.apache.axis2</groupId>
@@ -87,17 +91,12 @@
         <dependency>
             <groupId>com.squareup.moshi</groupId>
             <artifactId>moshi</artifactId>
-            <version>1.12.0</version>
+            <version>${moshi.version}</version>
         </dependency>
         <dependency>
             <groupId>com.squareup.moshi</groupId>
             <artifactId>moshi-adapters</artifactId>
-            <version>1.13.0</version>
-        </dependency>
-        <dependency>
-            <groupId>com.squareup.okio</groupId>
-            <artifactId>okio</artifactId>
-            <version>2.10.0</version>
+            <version>${moshi.version}</version>
         </dependency>
         <dependency>
             <groupId>commons-logging</groupId>