Portion of diff was dropped in the mappings update commit.
Also remove the option to remove invalid statistics. The server will
automatically do this now as of... 1.13?, our option wasn't even doing anything.
Per MC-138093 comments, ForkJoinPool uses unlimited threads if
parallelism is ever 1. A 2 core machine will end up with 1
with the change I had previously made, so bumped the min
to 2 so we will never trigger the unlimited thread situation.
This aligns the min back with Spigot, but allows use of more
threads on systems with more cores.
Spigot capped it to 2 threads. This bumps it back up to do
maxcores -2 with a max cap of 6.
A typical 4C8T system can use 6 threads and be done in 6 seconds.
Server owners can use system property to override, but this
improves the default.
