[Code Clean] Remove support of python3.9 (#163846)

As the title stated.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/163846
Approved by: https://github.com/ezyang

.ci/docker/manywheel/build_scripts/ssl-check.py

@@ -10,11 +10,6 @@ BAD_SSL = "https://self-signed.badssl.com"
 
 print("Testing SSL certificate checking for Python:", sys.version)
 
-if sys.version_info[:2] < (2, 7) or sys.version_info[:2] < (3, 4):
-    print("This version never checks SSL certs; skipping tests")
-    sys.exit(0)
-
-
 EXC = OSError
 
 print(f"Connecting to {GOOD_SSL} should work")

test/run_test.py

@@ -951,10 +951,7 @@ def test_openreg(test_module, test_directory, options):
 
 
 def test_distributed(test_module, test_directory, options):
-    # MPI tests are broken with Python-3.9
-    mpi_available = subprocess.call(
-        "command -v mpiexec", shell=True
-    ) == 0 and sys.version_info < (3, 9)
+    mpi_available = shutil.which("mpiexec")
     if options.verbose and not mpi_available:
         print_to_stderr("MPI not available -- MPI backend tests will be skipped")