Remove inappropriate check for a previous installation.

Original patch for bokek 0.5.0 (0.5.0-setup.patch).
Ported for bokeh 0.7.1 by Marius Brehler.

http://bugs.gentoo.org/527336

--- setup.py
+++ setup.py.new
@@ -348,7 +348,6 @@ path = abspath(dirname(__file__))
 
 print()
 if 'develop' in sys.argv:
-    check_remove_bokeh_install(site_packages)
     with open(path_file, "w+") as f:
         f.write(path)
     print("Installing Bokeh for development:")