Remove mentions of "reading change threshold".

... And the accompanying "Reading change threshold" section.

With the introduction of the "threshold check algorithm", this section is a
bit simplistic and is no longer necessary, as it only covers thresholds
provided by the device sensor or the operating system.

Author: Raphael Kubo da Costa

index.bs

@@ -513,8 +513,8 @@ thus user agents should not provide
 unnecessarily verbose readouts of sensors data.
 
 Implementations of concrete sensors may define a [=threshold check algorithm=]
-so that new readings that do not meet the [=reading change threshold=] when
-compared to the [=latest readings=] are discarded.
+so that new readings that do not differ enough from the [=latest readings=] are
+discarded.
 
 Implementations of concrete sensors may define a [=reading quantization
 algorithm=] to reduce the accuracy of the [=sensor readings=] received from a
@@ -725,19 +725,6 @@ define ways to uniquely identify each one.
     </pre>
 </div>
 
-## Reading change threshold ## {#concepts-reading-change-threshold}
-
-A [=platform sensor=] reports [=sensor readings|readings=] to the user agent considering
-the [=reading change threshold=].
-
-The <dfn>reading change threshold</dfn> refers to a value which indicates whether or
-not the changes in the [=device sensor=]'s measurements were significant enough to
-update the corresponding [=sensor readings=].
-
-The [=reading change threshold|threshold=] value depends on the surrounding software and hardware
-environment constraints, e.g., software power consumption optimizations or the underlying
-[=device sensor=]'s accuracy.
-
 ## Sampling Frequency and Reporting Frequency ## {#concepts-sampling-and-reporting-frequencies}
 
 For the purpose of this specification, <dfn>sampling frequency</dfn> for a [=platform sensor=] is
@@ -753,8 +740,12 @@ can support it.
 The [=sampling frequency=] differs from the [=requested sampling frequency=] in the following cases:
  - the [=requested sampling frequency=] exceeds upper or lower [=sampling frequency=] bounds
    supported by the underlying platform.
- - the [=reading change threshold|threshold=] value is significant so that some of the
-   [=device sensor=]'s measurements are skipped and the [=sensor readings=] are not updated.
+ - the operating system and/or the [=device sensor=] automatically discard
+   readings that do not differ enough (in absolute or relative terms) from the
+   previously reported ones via a hardware or operating system filter.
+ - the [=platform sensor=]'s associated [=sensor type=]'s [=threshold check
+   algorithm=] fails and the [=platform sensor=]'s [=latest readings=] are not
+   updated.
 
 The <dfn>reporting frequency</dfn> for a concrete {{Sensor}} object is defined as a frequency at which
 the "reading" event is [=fire an event|fired=] at this object.
@@ -819,8 +810,8 @@ A [=sensor type=] has a [=set/is empty|nonempty=] [=ordered set|set=] of associa
 
 A [=sensor type=] may have an associated <dfn export>threshold check
 algorithm</dfn>, which takes as arguments two separate [=sensor readings=] and
-determines if the difference between them is higher than an
-implementation-defined [=reading change threshold=].
+determines if they differ enough to cause a [=platform sensor=]'s [=latest
+reading=] map to be updated.
 
 A [=sensor type=] may have an associated <dfn export>reading quantization
 algorithm</dfn>, which takes a [=sensor reading=] and returns a less accurate