configury: silence warning on Solaris

revert r32501

Refs #4911
configury: silence warning on Solaris

 * remove config/ompi_config_solaris_threads.m4 which was dead code
 * check if pthreads work "as is" on all platforms including Solaris
   (FWIW, the test should have been skipped if Solaris threads are used
    and not if configure is ran on a Solaris box)

Refs #4911