timers: Remove unused __round_jiffies(_up)

Remove two trivial but long unused functions.

__round_jiffies() has been unused since 2008's
commit 9c133c46 ("Add round_jiffies_up and related routines")

__round_jiffies_up() has been unused since 2019's
commit 7ae3f6e1 ("powerpc/watchdog: Use hrtimers for per-CPU
heartbeat")

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250418200803.427911-1-linux@treblig.org