bpo-42029: Remove IRIX code

[vstinner]

IRIX code was slowy removed in Python 2.4 (--with-sgi-dl), Python 3.3
(Irix threads), and Python 3.7.

https://bugs.python.org/issue42029

[vstinner]

cc @kadler

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @vstinner for commit b3d5b3d 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[vstinner]

I'm not confident in my resource.getpagesize() change, so I test my PR on buildbots.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x RHEL8 3.x has failed when building commit 5776663.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/509/builds/260) and take a look at the build logs.
4. Check if the failure is related to this commit (5776663) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/509/builds/260

Failed tests:

• test_os
• test_multiprocessing_fork

Failed subtests:

• test_utime_current_old - test.test_os.UtimeTests
• test_utime_current - test.test_os.UtimeTests

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-rhel8-z/build/Lib/test/test_os.py", line 762, in test_utime_current_old
    self._test_utime_current(set_time)
  File "/home/dje/cpython-buildarea/3.x.edelsohn-rhel8-z/build/Lib/test/test_os.py", line 749, in _test_utime_current
    self.assertAlmostEqual(st.st_mtime, current,
AssertionError: 1603981504.2480948 != 1603981504.3209374 within 0.05 delta (0.07284259796142578 difference) : st_time=1603981504.2480948, current=1603981504.3209374, dt=-0.07284259796142578


Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-rhel8-z/build/Lib/test/test_os.py", line 756, in test_utime_current
    self._test_utime_current(set_time)
  File "/home/dje/cpython-buildarea/3.x.edelsohn-rhel8-z/build/Lib/test/test_os.py", line 749, in _test_utime_current
    self.assertAlmostEqual(st.st_mtime, current,
AssertionError: 1603981504.2480948 != 1603981504.318087 within 0.05 delta (0.0699923038482666 difference) : st_time=1603981504.2480948, current=1603981504.318087, dt=-0.0699923038482666