diff -r 79a967128055 -r b70c9697ab41 mercurial/configitems.py
--- a/mercurial/configitems.py	Tue Feb 15 05:20:46 2022 +0100
+++ b/mercurial/configitems.py	Fri Feb 11 16:52:48 2022 -0800
@@ -1042,11 +1042,6 @@
 )
 coreconfigitem(
     b'experimental',
-    b'mergetempdirprefix',
-    default=None,
-)
-coreconfigitem(
-    b'experimental',
     b'mmapindexthreshold',
     default=None,
 )