count-delta.c: comment fixes

There was a stale comment that explains why the old code could
undercount when delta data copied things around inside detination
buffer.  We do not use that kind of delta, so the comment does
not apply.

count-delta.c

@@ -16,11 +16,7 @@
  *
  * Number of bytes that are _not_ copied from the source is deletion,
  * and number of inserted literal bytes are addition, so sum of them
- * is the extent of damage.  xdelta can express an edit that copies
- * data inside of the destination which originally came from the
- * source.  We do not count that in the following routine, so we are
- * undercounting the source material that remains in the final output
- * that way.
+ * is the extent of damage.
  */
 int count_delta(void *delta_buf, unsigned long delta_size,
 		unsigned long *src_copied, unsigned long *literal_added)