Use the 'device sensor' term in the Scope section

The 'device sensor' term is defined and used within the
specification. Using it in the Scope section instead of
'local sensor' makes this section consistent with the rest
of the specification contents and also more clear.

This patch is a part of the effort for fixing the
[TAG review issues](w3c#303).

index.bs

@@ -155,8 +155,7 @@ explainer documents.
 <em>This section is non-normative</em>.
 
 The scope of this specification is currently limited
-to specifying primitives
-which enable expose data from local sensors.
+to specifying primitives which enable exposing data from [=device sensors=].
 
 Exposing remote sensors
 or sensors found on personal area networks (e.g. Bluetooth)