test-ssh: stop quoting dummyssh invocation for Windows

The other invocations aren't quoted, and Windows doesn't like the single quotes:

  diff --git a/tests/test-ssh.t b/tests/test-ssh.t
  --- a/tests/test-ssh.t
  +++ b/tests/test-ssh.t
  @@ -520,20 +520,8 @@ remote hook failure is attributed to rem
     $ echo "pretxnchangegroup.fail = python:$TESTTMP/failhook:hook" >> remote/.hg/hgrc

     $ hg -q --config ui.ssh="python '$TESTDIR/dummyssh'" clone ssh://user@dummy/remote hookout
  +  abort: no suitable response from remote hg!
  +  [255]
     $ cd hookout
  +  $TESTTMP.sh: line 264: cd: hookout: No such file or directory
     $ touch hookfailure
  -  $ hg -q commit -A -m 'remote hook failure'
  ....

tests/test-ssh-bundle1.t

@@ -524,11 +524,11 remote hook failure is attributed to rem
 
   $ echo "pretxnchangegroup.fail = python:$TESTTMP/failhook:hook" >> remote/.hg/hgrc
 
-  $ hg -q --config ui.ssh="python '$TESTDIR/dummyssh'" clone ssh://user@dummy/remote hookout
+  $ hg -q --config ui.ssh="python $TESTDIR/dummyssh" clone ssh://user@dummy/remote hookout
   $ cd hookout
   $ touch hookfailure
   $ hg -q commit -A -m 'remote hook failure'
-  $ hg --config ui.ssh="python '$TESTDIR/dummyssh'" push
+  $ hg --config ui.ssh="python $TESTDIR/dummyssh" push
   pushing to ssh://user@dummy/remote
   searching for changes
   remote: adding changesets

tests/test-ssh.t

@@ -519,11 +519,11 remote hook failure is attributed to rem
 
   $ echo "pretxnchangegroup.fail = python:$TESTTMP/failhook:hook" >> remote/.hg/hgrc
 
-  $ hg -q --config ui.ssh="python '$TESTDIR/dummyssh'" clone ssh://user@dummy/remote hookout
+  $ hg -q --config ui.ssh="python $TESTDIR/dummyssh" clone ssh://user@dummy/remote hookout
   $ cd hookout
   $ touch hookfailure
   $ hg -q commit -A -m 'remote hook failure'
-  $ hg --config ui.ssh="python '$TESTDIR/dummyssh'" push
+  $ hg --config ui.ssh="python $TESTDIR/dummyssh" push
   pushing to ssh://user@dummy/remote
   searching for changes
   remote: adding changesets