Revert "Make TaskThreads default on JRuby"
Revert "Make TaskThreads default on JRuby"

This reverts commit c78a5a3dd88ca9157b04849d295d4d27b6134f05.

TaskThreads are not ready for primetime :(

celluloid/celluloid,davydovanton/celluloid,kenichi/celluloid,mehta/celluloid,sideci-sample/sideci-sample-celluloid,olleolleolle/celluloid,jstoja/celluloid,jasonm23/celluloid,TiagoCardoso1983/celluloid,marshall-lee/celluloid,dilumn/celluloid,seuros/celluloid