vcs-svn: do not initialize report_buffer twice

vcs-svn: do not initialize report_buffer twice

When importing from a dump with deltas, first fast_export_init calls
buffer_fdinit, and then init_report_buffer calls fdopen once again
when processing the first delta.  The second initialization is
redundant and leaks a FILE *.

Remove the redundant on-demand initialization to fix this.
Initializing directly in fast_export_init is simpler and lets the
caller pass an int specifying which fd to use instead of hard-coding
REPORT_FILENO.

Signed-off-by: Dmitry Ivankov <divanorama@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>