[drlvm][threading] Removing APR extension functions

[Ilya Berezhniuk <il...@gmail.com>]

Hello everyone.

I've found that after recently committed H-3288 changes, several APR
extention functions located in 'vm/port/src/thread/linux/apr_thread_ext.c'
and 'vm/port/src/thread/win/apr_thread_ext.c' are not used anymore. All
other functions were rewritten in platform-dependant files of 'hythr' module
and named with 'os_' prefix.
There is one function which is currently used: apr_memory_rw_barrier().

I think we should remove unused functions with duplicating functionality.
apr_memory_rw_barrier() can be renamed in the same way to
os_memory_rw_barrier() and placed to platform-dependant files in 'hythr'
(because only 'hythr' uses this function).

I've created H-3482 and attached patch which does suggested changes.

-- 

Ilya