HOTFIX: remove exdot_cuda race condition
HOTFIX: remove exdot_cuda race condition

This bug manifested in rare crashes of simulations that were hard to
reproduce and happened seemingly without reason

mwiesenberger/feltor,feltor-dev/feltor,mwiesenberger/feltor,feltor-dev/feltor,mwiesenberger/feltor,feltor-dev/feltor,mwiesenberger/feltor,feltor-dev/feltor