task: address review comments for new helpers.

1. Merge state wise iterators and counters into
one function, where iteration/counting will happen
as per specified state.

2. address inconsistency between values of task state
macros in UEK-4 and later kernels.

Also, remove "is_task_struct_leaking" helper from this PR.
I have found that in UEK-5 with cgroups multiple task_stuct
slab caches are bing created and also the number of allocated
objects in them is different in drgn and crash. This needs
to be debugged first and then can be integrated via a separate
PR.

Signed-off-by: Imran Khan <[email protected]>

 Conflicts:
	drgn_tools/task.py