nfsd: Delete extraneous NFSv4 root checks

There are several NFSv4.1/4.2 server operation functions which
have unneeded checks for the NFSv4 root being set up.
The checks are not needed because the operations always follow
a Sequence operation, which performs the check.

This patch deletes these checks, simplifying the code so
that a future patch that fixes the checks to conform with
RFC5661 Sec. 2.6 will be less extension.

MFC after: 2 weeks