bpo-29506: Clarify deep copy note in copy module

The reference to administrative data was confusing to readers,
so this simplifies the note to explain that deep copying may copy
more then you intended, such as data that you expected to be
shared between copies.

Doc/library/copy.rst

@@ -47,8 +47,8 @@ copy operations:
 * Recursive objects (compound objects that, directly or indirectly, contain a
   reference to themselves) may cause a recursive loop.
 
-* Because deep copy copies *everything* it may copy too much, e.g.,
-  even administrative data structures that should be shared even between copies.
+* Because deep copy copies everything it may copy too much, such as data
+  which is intended to be shared between copies.
 
 The :func:`deepcopy` function avoids these problems by: