Fix use of non-existant reST role

Author: zware

buildslave.rst

@@ -85,9 +85,8 @@ For Windows:
     * Install the latest version of Python 2.7 from python.org.
     * Open a Command Prompt.
     * Execute ``python -m pip install pypiwin32 buildbot-slave`` (note that
-      :executable:`python.exe` is not added to :envvar:`PATH` by default,
-      making the ``python`` command accessible is left as an exercise for the
-      user).
+      ``python.exe`` is not added to :envvar:`PATH` by default, making the
+      ``python`` command accessible is left as an exercise for the user).
 
 In a terminal window for the buildbot user, issue the following commands (you
 can put the ``buildarea`` wherever you want to)::