convert: remove old ElementTree import cruft from darcs stable

convert: remove old ElementTree import cruft from darcs

All the `import elementtree` attempts seem to pre-date py2.5, when it was
brought into the standard library, and the manual `cElementTree` fast
implementation import has been unnecessary and deprecated since py3.3.

--- a/contrib/import-checker.py	Thu Jun 16 20:44:52 2022 +0200
+++ b/contrib/import-checker.py	Wed Jun 15 01:01:02 2022 +0100
@@ -47,6 +47,7 @@
     'mercurial.thirdparty.zope',
     'mercurial.thirdparty.zope.interface',
     'typing',
+    'xml.etree.ElementTree',
 )
 
 # Allow list of symbols that can be directly imported.

--- a/hgext/convert/darcs.py	Thu Jun 16 20:44:52 2022 +0200
+++ b/hgext/convert/darcs.py	Wed Jun 15 01:01:02 2022 +0100
@@ -8,6 +8,10 @@
 import os
 import re
 import shutil
+from xml.etree.ElementTree import (
+    ElementTree,
+    XMLParser,
+)
 
 from mercurial.i18n import _
 from mercurial import (
@@ -20,26 +24,6 @@
 
 NoRepo = common.NoRepo
 
-# The naming drift of ElementTree is fun!
-
-try:
-    import xml.etree.cElementTree.ElementTree as ElementTree
-    import xml.etree.cElementTree.XMLParser as XMLParser
-except ImportError:
-    try:
-        import xml.etree.ElementTree.ElementTree as ElementTree
-        import xml.etree.ElementTree.XMLParser as XMLParser
-    except ImportError:
-        try:
-            import elementtree.cElementTree.ElementTree as ElementTree
-            import elementtree.cElementTree.XMLParser as XMLParser
-        except ImportError:
-            try:
-                import elementtree.ElementTree.ElementTree as ElementTree
-                import elementtree.ElementTree.XMLParser as XMLParser
-            except ImportError:
-                pass
-
 
 class darcs_source(common.converter_source, common.commandline):
     def __init__(self, ui, repotype, path, revs=None):