Revert "Default to -H:-CompactingOldGen."

This reverts commit f405fcc.

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/SerialGCOptions.java

@@ -112,7 +112,7 @@ public Integer getValue(OptionValues values) {
     /** Query these options only through an appropriate method. */
     public static class ConcealedOptions {
         @Option(help = "Collect old generation by compacting in-place instead of copying.", type = OptionType.Expert) //
-        public static final HostedOptionKey<Boolean> CompactingOldGen = new HostedOptionKey<>(false, SerialGCOptions::validateCompactingOldGen);
+        public static final HostedOptionKey<Boolean> CompactingOldGen = new HostedOptionKey<>(true, SerialGCOptions::validateCompactingOldGen);
 
         @Option(help = "Determines if a remembered set is used, which is necessary for collecting the young and old generation independently.", type = OptionType.Expert) //
         public static final HostedOptionKey<Boolean> UseRememberedSet = new HostedOptionKey<>(true, SerialGCOptions::serialGCOnly);