blame: simplify 'setup_scoreboard' interface

blame: simplify 'setup_scoreboard' interface

The previous commit moved the initialization of 'sb.path' in
'builtin/blame.c::cmd_blame' before the call to
'blame.c::setup_scoreboard'. Since 'cmd_blame' is the only caller of
'setup_scoreboard', it is now unnecessary for 'setup_scoreboard' to
receive 'path' as a separate argument, as 'sb.path' is already
initialized.

Remove this argument from setup_scoreboard's interface and use the
'path' field of the 'sb' 'struct blame_scoreboard' instead.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>