pom: remove source/target configuration on maven-compiler-plugin

On Java 11, which we require for building, the compiler accepts
--release 8 and no longer requires -source or -target, so these are
unnecessary

runelite-jshell/pom.xml

@@ -73,8 +73,6 @@
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
                 <configuration>
-                    <source>11</source>
-                    <target>11</target>
                     <release>11</release>
                 </configuration>
             </plugin>