selftests/nolibc: simplify status printing

pad_spc() is only ever used to print the status message of testcases.
The line size is always constant, the return value is never used and the
format string is never used as such.

Remove all the unneeded logic and simplify the API and its users.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>