tests: replace cat.py with cat in test-histedit-fold-non-commute.t

tests/test-histedit-fold-non-commute.t

@@ -97,13 +97,7 fix up
   $ hg resolve --mark e
   (no more unresolved files)
   continue: hg histedit --continue
-  $ cat > cat.py <<EOF
-  > import sys
-  > print open(sys.argv[1]).read()
-  > print
-  > print
-  > EOF
-  $ HGEDITOR="python cat.py" hg histedit --continue 2>&1 | fixbundle | grep -v '2 files removed'
+  $ HGEDITOR=cat hg histedit --continue 2>&1 | fixbundle | grep -v '2 files removed'
   d
   ***
   does not commute with e
@@ -117,9 +111,6 fix up
   HG: branch 'default'
   HG: changed d
   HG: changed e
-  
-  
-  
   merging e
   warning: conflicts while merging e! (edit, then use 'hg resolve --mark')
   Fix up the change (pick 7b4e2f4b7bcd)