Parallel: Obsolete ParallelOldDeadWoodLimiterMean and ParallelOldDeadWoodLimiterStdDev

In full-gc, Parallel uses `ParallelOldDeadWoodLimiterMean` and `ParallelOldDeadWoodLimiterStdDev`, together with `MarkSweepDeadRatio`, to calculate the dead-wood percentage based on a normal distribution.

Both Serial and G1 use solely `MarkSweepDeadRatio` to control the maximum wasted space after a collection.

Remove those two statistical flags and interpret `MarkSweepDeadRatio` as the maximum wasted space in the old-gen would make Parallel full-gc more predictable, and also be consistent with Serial and G1.