nfsd: kill stale comment about simple_fill_super() requirements

That went into the tree back in 2005; the comment used to be true for
predecessor of simple_fill_super() that happened to live in nfsd; that one
didn't take care to skip the array entries with NULL ->name, so it could
not tolerate any gaps.  That had been fixed in 2003 when nfsd_fill_super()
had been abstracted into simple_fill_super(); if Neil's patch lived out
of tree during that time, he probably replaced the name of function when
rebasing it and didn't notice that restriction in question was no longer
there.

Acked-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>