nfsd: remove unused stats counters

nfsd: remove unused stats counters

[ Upstream commit 1b76d1df1a3683b6b23cd1c813d13c5e6a9d35e5 ]

Commit 501cb1849f86 ("nfsd: rip out the raparms cache") removed the
code that updates read-ahead cache stats counters,
commit 8bbfa9f3889b ("knfsd: remove the nfsd thread busy histogram")
removed code that updates the thread busy stats counters back in 2009
and code that updated filehandle cache stats was removed back in 2002.

Remove the unused stats counters from nfsd_stats struct and print
hardcoded zeros in /proc/net/rpc/nfsd.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>