ci: remove unnecessary distributionManagement section

The distributionManagement declared in the pom.xml files
interferes the upload to GCP ArtifactRegistry because it tries to
upload artifacts to google.oss.sonatype.org even when you try to
upload artifacts to GCP Artifact Registry.
The distributionManagement is already configured in the parent
POM at
https://github.com/googleapis/java-shared-config/blob/6d526a3129f585338b14dab8f041e56dbaae4cd5/native-image-shared-config/pom.xml#L42
No need redeclare in these pom.xml files.

java-common-protos/pom.xml

@@ -31,16 +31,6 @@
   <organization>
     <name>Google LLC</name>
   </organization>
-  <distributionManagement>
-    <snapshotRepository>
-      <id>sonatype-nexus-snapshots</id>
-      <url>https://google.oss.sonatype.org/content/repositories/snapshots</url>
-    </snapshotRepository>
-    <repository>
-      <id>sonatype-nexus-staging</id>
-      <url>https://google.oss.sonatype.org/service/local/staging/deploy/maven2/</url>
-    </repository>
-  </distributionManagement>
   <licenses>
     <license>
       <name>Apache-2.0</name>

java-iam/pom.xml

@@ -31,16 +31,6 @@
   <organization>
     <name>Google LLC</name>
   </organization>
-  <distributionManagement>
-    <snapshotRepository>
-      <id>sonatype-nexus-snapshots</id>
-      <url>https://google.oss.sonatype.org/content/repositories/snapshots</url>
-    </snapshotRepository>
-    <repository>
-      <id>sonatype-nexus-staging</id>
-      <url>https://google.oss.sonatype.org/service/local/staging/deploy/maven2/</url>
-    </repository>
-  </distributionManagement>
   <licenses>
     <license>
       <name>Apache-2.0</name>