Correct a pom.xml problem that was failing CI builds.

Remove the unneeded `org.sonatype.oss:oss-parent` parent in two places. This was producing errors like this:

```
Error:  Failed to execute goal org.apache.maven.plugins:maven-invoker-plugin:3.2.2:install (integration-test) on project auto-value-annotations: Failed to install project parents: MavenProject: com.google.auto.value:auto-value-annotations:HEAD-SNAPSHOT @ /home/runner/work/auto/auto/value/annotations/pom.xml: Failed to install POM: MavenProject: org.sonatype.oss:oss-parent:7 @ /home/runner/.m2/repository/org/sonatype/oss/oss-parent/7/oss-parent-7.pom: Failed to install artifact: org.sonatype.oss:oss-parent:pom:7: Failed to install artifact org.sonatype.oss:oss-parent:pom:7: cannot install /home/runner/.m2/repository/org/sonatype/oss/oss-parent/7/oss-parent-7.pom to same path -> [Help 1]
```

According to https://github.com/sonatype/oss-parents

> This project is no longer active or supported. We suggest to manage parent POM files for your own organization as needed. The POM files from this project no longer work with latest Maven and/or Java versions.

I don't think we were actually using anything from that parent, except maybe a release plugin.

RELNOTES=n/a
PiperOrigin-RevId: 395095285

factory/pom.xml

@@ -19,12 +19,6 @@
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
   <modelVersion>4.0.0</modelVersion>
 
-  <parent>
-    <groupId>org.sonatype.oss</groupId>
-    <artifactId>oss-parent</artifactId>
-    <version>7</version>
-  </parent>
-
   <groupId>com.google.auto.factory</groupId>
   <artifactId>auto-factory</artifactId>
   <version>HEAD-SNAPSHOT</version>

value/pom.xml

@@ -18,12 +18,6 @@
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
   <modelVersion>4.0.0</modelVersion>
 
-  <parent>
-    <groupId>org.sonatype.oss</groupId>
-    <artifactId>oss-parent</artifactId>
-    <version>7</version>
-  </parent>
-
   <groupId>com.google.auto.value</groupId>
   <artifactId>auto-value-parent</artifactId>
   <version>HEAD-SNAPSHOT</version>