check for markdown no longer needed, closes #3610

After #3582 was merged, we no longer depend on a python version of
markdown

setup.py

@@ -278,7 +278,7 @@ if 'setuptools' in sys.modules:
         doc = 'Sphinx>=0.3',
         test = 'nose>=0.10.1',
         notebook = ['tornado>=2.0', 'pyzmq>=2.1.11', 'jinja2'],
-        nbconvert = ['pygments', 'markdown', 'jinja2', 'Sphinx>=0.3']
+        nbconvert = ['pygments', 'jinja2', 'Sphinx>=0.3']
     )
     requires = setup_args.setdefault('install_requires', [])
     setupext.display_status = False

setupbase.py

@@ -355,7 +355,7 @@ def check_for_dependencies():
         check_for_sphinx, check_for_pygments,
         check_for_nose, check_for_pexpect,
         check_for_pyzmq, check_for_readline,
-        check_for_jinja2, check_for_markdown
+        check_for_jinja2
     )
     print_line()
     print_raw("BUILDING IPYTHON")
@@ -374,7 +374,6 @@ def check_for_dependencies():
     check_for_pyzmq()
     check_for_readline()
     check_for_jinja2()
-    check_for_markdown()
 
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 # VCS related