The function `set_ident` in `filter-branch` exported the variables
GIT_(AUTHOR|COMMITTER)_(NAME|EMAIL|DATE) at least since 6f6826c52b in 2007.
Therefore the filter scripts don't need to re-eport them again.
Signed-off-by: Andreas Heiduk <asheiduk@gmail.com> Reviewed-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>