printk: Remove pr_cont_once()

pr_cont_once() does not make sense; at least emitting module name using
pr_fmt() into middle of a line (after e.g. pr_info_once()) does not make
sense. Let's remove unused pr_cont_once().

Link: https://lore.kernel.org/r/20200524153243.11690-1-penguin-kernel@I-love.SAKURA.ne.jp


Cc: Joe Perches <joe@perches.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>