doc: modernize usage of “disk” and “core”

In documentation and comments, don’t assume that secondary storage
devices are disk devices.  Similarly, don’t assume that main memory
uses magnetic cores, which became obsolete in the 1970s.
* src/du.c (usage):
* src/ls.c (usage):
* src/shred.c (usage): Reword to avoid “disk” in usage messages.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/copy.h b/src/copy.h
index a97089137..68d52e1ce 100644
--- a/src/copy.h
+++ b/src/copy.h
@@ -41,7 +41,7 @@ enum Sparse_type
      create a corresponding hole in DEST.  There is a performance penalty
      here because CP has to search for holes in SRC.  But if the holes are
      big enough, that penalty can be offset by the decrease in the amount
-     of data written to disk.   */
+     of data written to the file system.   */
   SPARSE_ALWAYS
 };