Remove fork_context from llnl.util.lang (#25620)

This object was introduced in #18124, and was later superseded by
#18205 and removed any use if the object.

lib/spack/llnl/util/lang.py

@@ -7,7 +7,6 @@
 
 import functools
 import inspect
-import multiprocessing
 import os
 import re
 import sys
@@ -31,23 +30,6 @@
 ignore_modules = [r'^\.#', '~$']
 
 
-# On macOS, Python 3.8 multiprocessing now defaults to the 'spawn' start
-# method. Spack cannot currently handle this, so force the process to start
-# using the 'fork' start method.
-#
-# TODO: This solution is not ideal, as the 'fork' start method can lead to
-# crashes of the subprocess. Figure out how to make 'spawn' work.
-#
-# See:
-# * https://github.com/spack/spack/pull/18124
-# * https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods  # noqa: E501
-# * https://bugs.python.org/issue33725
-if sys.version_info >= (3,):  # novm
-    fork_context = multiprocessing.get_context('fork')
-else:
-    fork_context = multiprocessing
-
-
 def index_by(objects, *funcs):
     """Create a hierarchy of dictionaries by splitting the supplied
     set of objects on unique values of the supplied functions.