tests: un-nest the `order` repo in test-rebase-scenario-global

This wasn't hurting anything, but it's more in line with how we manage
other tests.

tests/test-rebase-scenario-global.t

@@ -773,7 +773,7 b' Test that rebase is not confused by $CWD'
 Get back to the root of cwd-vanish. Note that even though `cd ..`
 works on most systems, it does not work on FreeBSD 10, so we use an
 absolute path to get back to the repository.
-  $ cd $TESTTMP/cwd-vanish
+  $ cd $TESTTMP
 
 Test that rebase is done in topo order (issue5370)
 
@@ -819,7 +819,7 b' Test that rebase is done in topo order ('
   rebasing 4:82ae8dc7a9b7 "E"
   rebasing 3:ab709c9f7171 "D"
   rebasing 5:412b391de760 "F"
-  saved backup bundle to $TESTTMP/cwd-vanish/order/.hg/strip-backup/76035bbd54bd-e341bc99-backup.hg (glob)
+  saved backup bundle to $TESTTMP/order/.hg/strip-backup/76035bbd54bd-e341bc99-backup.hg (glob)
 
   $ hg tglog
   o  6: 'F'
@@ -840,7 +840,7 b' Test that rebase is done in topo order ('
 Test experimental revset
 ========================
 
-  $ cd ..
+  $ cd ../cwd-vanish
 
 Make the repo a bit more interesting