build: removing unnecessary maven-compiler-plugin configuration (#1761)

The maven-compiler-plugin configuration is already defined in
the shared config pom.xml. This project does not need to declare
the plugin and its configuration.
https://togithub.com/googleapis/java-shared-config/blob/778a547a09de71dbf9e5a42b155f12d15c319864/pom.xml#L738

README.md

@@ -52,20 +52,20 @@ If you are using Maven without the BOM, add this to your dependencies:
 If you are using Gradle 5.x or later, add this to your dependencies:
 
 ```Groovy
-implementation platform('com.google.cloud:libraries-bom:26.23.0')
+implementation platform('com.google.cloud:libraries-bom:26.24.0')
 
 implementation 'com.google.cloud:google-cloud-pubsub'
 ```
 If you are using Gradle without BOM, add this to your dependencies:
 
 ```Groovy
-implementation 'com.google.cloud:google-cloud-pubsub:1.125.4'
+implementation 'com.google.cloud:google-cloud-pubsub:1.125.5'
 ```
 
 If you are using SBT, add this to your dependencies:
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-pubsub" % "1.125.4"
+libraryDependencies += "com.google.cloud" % "google-cloud-pubsub" % "1.125.5"
 ```
 <!-- {x-version-update-end} -->
 
@@ -408,7 +408,7 @@ 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-pubsub/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-pubsub.svg
-[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-pubsub/1.125.4
+[maven-version-link]: https://central.sonatype.com/artifact/com.google.cloud/google-cloud-pubsub/1.125.5
 [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

google-cloud-pubsub/pom.xml

@@ -180,24 +180,6 @@
       </plugins>
     </pluginManagement>
     <plugins>
-      <plugin>
-        <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.11.0</version>
-        <configuration>
-          <source>1.8</source>
-          <target>1.8</target>
-          <encoding>UTF-8</encoding>
-          <compilerArgument>-Xlint:unchecked</compilerArgument>
-          <annotationProcessorPaths>
-            <path>
-              <groupId>com.google.auto.value</groupId>
-              <artifactId>auto-value</artifactId>
-              <version>${auto-value-annotation.version}</version>
-            </path>
-          </annotationProcessorPaths>
-        </configuration>
-      </plugin>
-
       <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>flatten-maven-plugin</artifactId>