time_stats: Kill TIME_STATS_HAVE_QUANTILES

We have 4 spare bytes next to the spinlock, no need for bit stuffing

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>