stress2/fullpath2: Clean up the vn_fullpath DTrace one-liner

• Remove -w; there is no need for destructive actions here.
• Remove the glob from before "vn_fullpath"; the probe description matches vn_fullpath only anyway, so there is no need for the glob here.

PR 288222
Reviewed by: christos
Approved by: christos (mentor)
Fixes: 113f2f0c76a7 stress2: Updated dtrace comment
Differential Revision: https://reviews.freebsd.org/D51341