gh-110014: Include explicitly <unistd.h> header (#110155)

* Remove unused <locale.h> includes.
* Remove unused <fcntl.h> include in traceback.h.
* Remove redundant <assert.h> and <stddef.h> includes. They  are already
  included by "Python.h".
* Remove <object.h> include in faulthandler.c. Python.h already includes it.
* Add missing <stdbool.h> in pycore_pythread.h if HAVE_PTHREAD_STUBS
  is defined.
* Fix also warnings in pthread_stubs.h: don't redefine macros if they
  are already defined, like the __NEED_pthread_t macro.