Reword is-deeply

Do not say it uses `eqv` operator. What it uses is an internal detail.

Addresses https://rt.perl.org/Ticket/Display.html?id=130362

doc/Language/testing.pod6

@@ -361,10 +361,10 @@ tested independently, and the C<is-approx> test will succeed only if both pass.
 
 =item X<is-deeply($value, $expected, $description?)|is-deeply>
 
-Marks a test as passed if C<$value> and C<$expected> compare positively with
-the L<eqv operator|/routine/eqv>. This is the best way to check for equality of
-(deep) data structures. The function accepts an optional C<$description> of
-the test.
+Marks a test as passed if C<$value> and C<$expected> are equivalent, using the
+same semantics as the L<eqv operator|/routine/eqv>. This is the best way to
+check for equality of (deep) data structures. The function accepts an optional
+C<$description> of the test.
 
 =begin code
 use v6;