refactor: remove unnecessary compiler tag comments from pom.xml (#10340)

Author: Kef131

appengine-java8/metadata/pom.xml

@@ -33,12 +33,10 @@ Copyright 2017 Google Inc.
     <version>1.2.0</version>
   </parent>
 
-  <!-- [START compiler] -->
   <properties>
     <maven.compiler.target>1.8</maven.compiler.target>
     <maven.compiler.source>1.8</maven.compiler.source>
   </properties>
-  <!-- [END compiler] -->
 
   <dependencyManagement>
     <dependencies>