tests: mem_protect: delete duplicate test

test_mem_part_inherity_by_child_thr duplicates logic already
present in test_permission_inheritance. That test puts a
buffer called 'inherit_buf' in 'inherit_memory_partition'
and shows that it is accessible by a child thread by
writing to it.

Delete this unnecessary test.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>