hrtimer: Remove unused header include

seq_file.h does not need to be included, so remove it.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190607174253.27403-1-tiny.windzz@gmail.com