Delete some comment or messages of keystone_data.sh(removed)

As files/keystone_data.sh has been removed in the commit
https://review.openstack.org/#/c/79366/, we should remove some
related documations and comments.

Change-Id: I7802d0052fa28d8debb7f361d36a4f108869554c
diff --git a/doc/source/configuration.rst b/doc/source/configuration.rst
index d70d3da..9ba657a 100644
--- a/doc/source/configuration.rst
+++ b/doc/source/configuration.rst
@@ -393,7 +393,7 @@
         KEYSTONE_CATALOG_BACKEND=template
 
 DevStack's default configuration in ``sql`` mode is set in
-``files/keystone_data.sh``
+``lib/keystone``
 
 
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