No code in diff.c sets DIFF_SYMBOL_MOVED_LINE except in
mark_color_as_moved(), so it is redundant to clear it for the current
line. Therefore, clear it only for previous lines.
This makes a refactoring in a subsequent patch easier.
Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>