MT#7431 Force strip getarch + getos files in ngcp-sems-libsems1-dev

Addressing:

| E: ngcp-sems-libsems1-dev: unstripped-binary-or-object usr/include/sems/compat/getarch
| E: ngcp-sems-libsems1-dev: unstripped-binary-or-object usr/include/sems/compat/getos

dh_strip doesn't work as reliable as lintian (e.g.
see #35733 and #468333 in Debian's BTS), so instruct
debian/rules to explicitly strip those files.