Remove a misleading java.version from the top-level pom.xml.

This isn't actually used for anything, and might mislead readers into thinking that Java 8 is supported.

PiperOrigin-RevId: 891322036

Author: eamonnmcmanus

pom.xml

@@ -85,7 +85,6 @@
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-    <java.version>1.8</java.version>
     <guava.version>32.1.3-jre</guava.version>
     <truth.version>1.4.0</truth.version>
     <jspecify.version>1.0.0</jspecify.version>
@@ -191,8 +190,6 @@
       <plugin>
         <artifactId>maven-compiler-plugin</artifactId>
         <configuration>
-          <source>${java.version}</source>
-          <target>${java.version}</target>
           <encoding>UTF-8</encoding>
           <compilerArgs>
             <!-- compile-time arguments for google-java-format -->