treewide: use scols printf api where possible

treewide: use scols printf api where possible

Everywhere a string generated with xasprintf() is directly passed to
scols_line_refer_data(), use scols_line_sprintf() to remove the need for
an intermediate buffer.

Replace the (now redundant) private scols_line_asprintf() function.

Signed-off-by: Robin Jarry <robin@jarry.cc>