games/netradiant: fix packaging on powerpc64

[pkubaj]

Summary

After the last update, this port doesn't need replacing ARCH on powerpc64 and doing it actually breaks packaging:
pkg-static: Unable to access file /wrkdirs/usr/ports/games/netradiant/work/stage/usr/local/share/netradiant/heretic2/h2data.powerpc:No such file or directory
pkg-static: Unable to access file /wrkdirs/usr/ports/games/netradiant/work/stage/usr/local/share/netradiant/q2map.powerpc:No such file or directory
pkg-static: Unable to access file /wrkdirs/usr/ports/games/netradiant/work/stage/usr/local/share/netradiant/q3data.powerpc:No such file or directory
pkg-static: Unable to access file /wrkdirs/usr/ports/games/netradiant/work/stage/usr/local/share/netradiant/q3map2.powerpc:No such file or directory
pkg-static: Unable to access file /wrkdirs/usr/ports/games/netradiant/work/stage/usr/local/share/netradiant/qdata3.powerpc:No such file or directory
pkg-static: Unable to access file /wrkdirs/usr/ports/games/netradiant/work/stage/usr/local/share/netradiant/radiant.powerpc:No such file or directory

[tcberner]