configitems: register the 'experimental.effect-flags' config

mercurial/configitems.py

@@ -348,6 +348,9 b" coreconfigitem('experimental', 'mmapinde"
 coreconfigitem('experimental', 'nonnormalparanoidcheck',
     default=False,
 )
+coreconfigitem('experimental', 'effect-flags',
+    default=False,
+)
 coreconfigitem('experimental', 'stabilization',
     default=list,
     alias=[('experimental', 'evolution')],

mercurial/obsolete.py

@@ -1049,8 +1049,7 b' def createmarkers(repo, relations, flag='
 
     # Effect flag metadata handling
     saveeffectflag = repo.ui.configbool('experimental',
-                                        'effect-flags',
-                                        False)
+                                        'effect-flags')
 
     tr = repo.transaction('add-obsolescence-marker')
     try: