build: do not declare javadoc plugin version (#1518)

Author: alicejli

README.md

@@ -33,13 +33,13 @@ If you are using Maven, add this to your pom.xml file:
 If you are using Gradle without BOM, add this to your dependencies:
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-pubsublite:1.12.14'
+implementation 'com.google.cloud:google-cloud-pubsublite:1.12.15'
 ```
 
 If you are using SBT, add this to your dependencies:
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-pubsublite" % "1.12.14"
+libraryDependencies += "com.google.cloud" % "google-cloud-pubsublite" % "1.12.15"
 ```
 <!-- {x-version-update-end} -->
 
@@ -483,7 +483,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-pubsublite/java11.html
 [stability-image]: https://img.shields.io/badge/stability-stable-green
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/google-cloud-pubsublite.svg
-[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-pubsublite/1.12.14
+[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-pubsublite/1.12.15
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication
 [auth-scopes]: https://developers.google.com/identity/protocols/oauth2/scopes
 [predefined-iam-roles]: https://cloud.google.com/iam/docs/understanding-roles#predefined_roles

pom.xml

@@ -127,7 +127,6 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
-        <version>3.6.0</version>
         <configuration>
           <source>8</source>
           <links combine.self="override">
@@ -208,7 +207,6 @@
           <plugin>
             <groupId>org.apache.maven.plugins</groupId>
             <artifactId>maven-javadoc-plugin</artifactId>
-            <version>3.6.0</version>
             <configuration>
               <excludePackageNames>com.google.cloud.pubsublite.cloudpubsub.internal:com.google.cloud.pubsublite.internal:com.google.cloud.pubsublite.internal.testing:com.google.cloud.pubsublite.internal.wire</excludePackageNames>
             </configuration>