[SPARK-3068]remove MaxPermSize option for jvm 1.8

In JVM 1.8.0, MaxPermSize is no longer supported.
In spark `stderr` output, there would be a line of

    Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=128m; support was removed in 8.0

Is all this code and munging in case JAVA_HOME is not the same Java as the Worker was started with? Otherwise it seems we could just do `sys.env("java.version")`.