Replace "copied back" with "available"

Descriptions of accessors elsewhere in the specification say that functions
block "until data is available", as not all implementations of accessors are
guaranteed or required to copy data.

adoc/chapters/programming_interface.adoc

@@ -6254,7 +6254,7 @@ There are several different {cpp} classes that implement accessors:
 
 Accessor objects must always be constructed in host code, either in
 <<command-group-scope>> or in <<application-scope>>.  Whether the constructor
-blocks until data has been copied back depends on the type of accessor.  Those
+blocks until data is available depends on the type of accessor.  Those
 accessors which provide access to data within a <<command>> do not block.
 Instead, these accessors define a requirement which influences the scheduling
 of the <<command>>.  Those accessors which provide access to data from host