os::release_memory_special (terrible name) releases memory backed by explicit (non-THP) large pages on Linux.

Its only point (and the reason why one did not just os::release_memory) was to handle the case where explicit large pages on Linux were allocated not with mmap but with system V shared memory.

We removed the use of system V shared memory with JDK-8261894. Since than, on the two platforms where we have explicit large pages (windows and linux), os::release_memory_special just effectively calls os::release_memory.

So we may just as well get rid of it completely and replace uses with os::release_memory.