mpi3mr: Remove -g

This -g was introduce when I didn't review all the cahnges to mpi3mr I
was MFCing. Remove it. This is a direct commit.

PR: 249068
Fixes: 80b069913d496
Sponsored by: Netflix
Approved by: re (cperciva)
(cherry picked from commit 22ebbdea3f33fdeae5ee83077ea9c25979705f2f)