vfs cache: retire dothits and dotdothits counters

They demonstrate nothing, and in case of dotdot they are not even hits.
This is just a count of lookups with "..", which are not worth
mentioniong.

(cherry picked from commit bb124a0f611a1288c8496e3b33494f23ba929ca1)
(cherry picked from commit 0cf6ebad73640a20fe99adacba635e2630be5d08)

Approved by: re (gjb