Revert "Increase parallelism in dm" (#578)

Here's the list of openmpvv fails (across OMP 4.5, 5.0, 5.1, 5.2):
test_target_taskloop_shared.c
test_target_teams_distribute_parallel_for_if_parallel_modifier.c
declare_target_base_and_derived_class.cpp
declare_target_base_class.cpp
test_loop_bind_device.c
test_loop_nested_device.c
test_loop_nested_device.F90
test_master_taskloop_device.c
test_master_taskloop_simd_device.c
test_parallel_master_device.c
test_parallel_master_taskloop_device.c
test_parallel_master_taskloop_simd_device.c
test_target_depend_lvalue_func.cpp
test_target_depend_lvalue_ptr.cpp
test_target_depend_lvalue_ternary.cpp
test_target_task_depend_mutexinoutset.c
test_depend_inout_omp_all_memory.c
test_target_depend_out_omp_all_memory.c
test_taskloop_simd_order_reproducible_device.c
test_taskloop_simd_order_unconstrained_device.c
test_task_target_default_firstprivate.c
test_target_VirFunc.cpp

smoke-dev:
clang-nested-parallel-for
red_bug_51
xteam-red-sched-default-option

All runtime fails with the same memory fault signature Michael posted
earlier.

This reverts commit 2f0e563.

Author: ronlieb