Remove BDB legacy code from FSFS: We shall stream file txdelta windows
directly to the APR file instead of buffering them in an intermediate
stream.

apply_textdelta used double buffering for the output.  With APR files
being buffered, there is no need to collect the txdelta windows in a
string buffer before writing them to disk.  Also, there is BDB-like
DB logging that might not like small writes.

* subversion/libsvn_fs_fs/tree.c
  (WRITE_BUFFER_SIZE): Drop.
  (txdelta_baton_t): Remove intermediate stream.
  (write_to_string): Drop obsolete writer function for intermediate stream.
  (window_consumer): No copying from intermediate to output stream needed.
                     Also, the delta receiver stream gets closed automtically
                     - now it's identical with our output stream.
  (apply_textdelta): No intermediate stream to create; write txdelta output
                     directly to our output stream.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1590416 13f79535-47bb-0310-9956-ffa450edef68