math/levmar: fix installation

Port uses <bsd.lib.mk>, which desires STRIP=${STRIP}, but we have
started to set STRIP=${STRIP_CMD} in MAKE_ENV a while ago.
Override this bogus setting in MAKE_ARGS to fix installation.

MFH: 2026Q2
See also: D55509
Approved by: portmgr (build fix blanket)

(cherry picked from commit 6128bc949139a0d000a3365465c9650a6fb5b2f9)