Remove vfs_statfs and vnode_mount macros from NFS
These macro definitions are no longer needed as the NFS OSX port is long
dead. The vfs_statfs macro conflicts with the vfsops field of the same
name.
Submitted by: shivank@
Reviewed by: rmacklem
MFC after: 2 weeks
Sponsored by: Google, Inc. (GSoC 2020)
Differential Revision: https://reviews.freebsd.org/D25263