Partially revert 9efe1a721, strip_tags improvements

The new regex seems not stable enough for being released. Stripping
with regex might need reevaluation for the next release.
Refs #19237.

tests/regressiontests/utils/html.py

@@ -65,7 +65,6 @@ class TestUtilsHtml(unittest.TestCase):
             ('<f', '<f'),
             ('</fe', '</fe'),
             ('<x>b<y>', 'b'),
-            ('a<p onclick="alert(\'<test>\')">b</p>c', 'abc'),
             ('a<p a >b</p>c', 'abc'),
             ('d<a:b c:d>e</p>f', 'def'),
         )