This completes the work done in 5.0 to remove mit_pthread support (most was pulled in 5.0, but there were some pieces left in the tree)


include/my_global.h:
  mit_thread removal
include/my_pthread.h:
  mit_thread removal
mysys/my_file.c:
  mit_thread removal
mysys/my_pthread.c:
  Removal of mit_thread
mysys/my_thr_init.c:
  Removal of mit_thread