7816 remove static unused variable in zfs_vfsops.c

illumos/illumos-gate@2e972bf18f2d3dc8a060f336db39dc8432ee887c
https://github.com/illumos/illumos-gate/commit/2e972bf18f2d3dc8a060f336db39dc8432ee887c

https://www.illumos.org/issues/7816

found by gcc6 build unused static variable:
-static const fs_operation_def_t zfs_vfsops_eio_template[] = {
-    VFSNAME_FREEVFS,    { .vfs_freevfs =  zfs_freevfs },
-    NULL,            NULL
-};

Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed by: Andy Stormont astormont@racktopsystems.com
Reviewed by: Pavel Zakharov <pavel.zakharov@delphix.com>
Approved by: Dan McDonald <danmcd@omniti.com>
Author: Igor Kozhukhov <igork@argotech.io>