Revert 83784 adding functools.lru_cache() to the re module.

The problem is that the re module is imported by sysconfig
and re needs functools which uses collections.OrderedDict()
but the _collectionsmodule.c code is not yet constructed
at this point in the build.

The likely best solution will be to include _collections
as part of the static build before the rest of the
boot-strapping.

Lib/test/test_re.py

@@ -875,8 +875,70 @@ def run_re_tests():
                     print('=== Fails on unicode-sensitive match', t)
 
 
+class ReCacheTests(unittest.TestCase):
+    """These tests are specific to the re._shrink_cache implementation."""
+
+    def setUp(self):
+        self._orig_maxcache = re._MAXCACHE
+
+    def tearDown(self):
+        re._MAXCACHE = self._orig_maxcache
+
+    def test_compile_cache_overflow(self):
+        # NOTE: If a profiler or debugger is tracing code and compiling
+        # regular expressions while tracing through this test... expect
+        # the test to fail.  This test is not concurrency safe.
+
+        # Explicitly fill the caches.
+        re._MAXCACHE = 20
+        max_cache = re._MAXCACHE
+        unique_chars = tuple(chr(char_num) for char_num in
+                             range(b'a'[0], b'a'[0]+max_cache))
+        re._cache.clear()
+        for char in unique_chars:
+            re._compile(char, 0)
+        self.assertEqual(max_cache, len(re._cache))
+        re._cache_repl.clear()
+        for char in unique_chars:
+            re._compile_repl(char*2, char)
+        self.assertEqual(max_cache, len(re._cache_repl))
+
+        # Overflow both caches and make sure they have extra room left
+        # afterwards as well as having more than a single entry.
+        re._compile('A', 0)
+        self.assertLess(len(re._cache), max_cache)
+        self.assertGreater(len(re._cache), 1)
+        re._compile_repl('A', 'A')
+        self.assertLess(len(re._cache_repl), max_cache)
+        self.assertGreater(len(re._cache_repl), 1)
+
+    def test_shrink_cache_at_limit(self):
+        cache = dict(zip(range(6), range(6)))
+        re._shrink_cache(cache, 6, divisor=3)
+        self.assertEqual(4, len(cache))
+
+    def test_shrink_cache_empty(self):
+        cache = {}
+        re._shrink_cache(cache, 6, divisor=3)
+        # Cache was empty, make sure we didn't raise an exception.
+        self.assertEqual(0, len(cache))
+
+    def test_shrink_cache_overflowing(self):
+        cache = dict(zip(range(6), range(6)))
+        re._shrink_cache(cache, 4, divisor=2)
+        # Cache was larger than the maximum, be sure we shrunk to smaller.
+        self.assertEqual(2, len(cache))
+
+    def test_shrink_cache_underflow(self):
+        cache = dict(zip(range(6), range(6)))
+        # No shrinking to do.
+        re._shrink_cache(cache, 9, divisor=3)
+        self.assertEqual(6, len(cache))
+
+
 def test_main():
     run_unittest(ReTests)
+    run_unittest(ReCacheTests)
     run_re_tests()
 
 if __name__ == "__main__":