Revert "[3.7] bpo-34589: Add -X coerce_c_locale option; C locale coercion off by default (GH-9379)" (GH-9416)

This reverts commit 144f1e2c6f4a24bd288c045986842c65cc289684.
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 9155afc..27f7590 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -656,8 +656,9 @@
 
     def c_locale_get_error_handler(self, locale, isolated=False, encoding=None):
         # Force the POSIX locale
-        env = dict(os.environ)
+        env = os.environ.copy()
         env["LC_ALL"] = locale
+        env["PYTHONCOERCECLOCALE"] = "0"
         code = '\n'.join((
             'import sys',
             'def dump(name):',
@@ -667,10 +668,7 @@
             'dump("stdout")',
             'dump("stderr")',
         ))
-        args = [sys.executable,
-                "-X", "utf8=0",
-                "-X", "coerce_c_locale=0",
-                "-c", code]
+        args = [sys.executable, "-c", code]
         if isolated:
             args.append("-I")
         if encoding is not None: