obsolete: clean createmarkers part about operation

obsolete: clean createmarkers part about operation

I will add another experiment in createmarkers, add a comment and some blank
lines for aesthetic sake.

Differential Revision: https://phab.mercurial-scm.org/D532

--- a/mercurial/obsolete.py	Sat Sep 30 12:58:06 2017 -0400
+++ b/mercurial/obsolete.py	Thu Jul 06 14:46:07 2017 +0200
@@ -1028,10 +1028,13 @@
         metadata = {}
     if 'user' not in metadata:
         metadata['user'] = repo.ui.username()
+
+    # Operation metadata handling
     useoperation = repo.ui.configbool('experimental',
         'stabilization.track-operation')
     if useoperation and operation:
         metadata['operation'] = operation
+
     tr = repo.transaction('add-obsolescence-marker')
     try:
         markerargs = []