Remove fast_memcpy and replace it with standard memcpy.

In the long gone past, clients and FSFS repositories used self-delta
within their txdelta data.  That created patterning copies as well
as other short-length copy ops.  Since then, these formats have become
much less prevalent, caching has reduced the need for fast parsing
and compiler intrinsics have improved.  Not using standard memcpy
doesn't by us much anymore.

* subversion/libsvn_delta/text_delta.c
  (fast_memcpy): Remove.
  (patterning_copy,
   svn_txdelta_apply_instructions): Call memcpy instead.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1618841 13f79535-47bb-0310-9956-ffa450edef68