Fix modules.rst doc build warning.

lib/spack/docs/Makefile

@@ -71,7 +71,7 @@ help:
 	@echo "  doctest    to run all doctests embedded in the documentation (if enabled)"
 
 clean:
-	-rm -f package_list.rst command_index.rst
+	-rm -f package_list.rst command_index.rst modules.rst
 	-rm -rf $(BUILDDIR)/* $(APIDOC_FILES)
 
 html:

lib/spack/docs/conf.py

@@ -71,9 +71,6 @@
 # Generate package list using spack command
 #
 with open('package_list.rst', 'w') as plist_file:
-    subprocess.check_output(
-        [spack_root + '/bin/spack', 'package-list'])
-
     subprocess.Popen(
         [spack_root + '/bin/spack', 'package-list'], stdout=plist_file)
 
@@ -97,6 +94,7 @@
 
 # Run sphinx-apidoc
 sphinx_apidoc(['-T', '-o', '.', '../spack'])
+os.remove('modules.rst')
 
 #
 # Exclude everything in spack.__all__ from indexing.  All of these