emulators/rpcs3: don't embed default RPATH

$ readelf -d $(which rpcs3) | fgrep PATH
0x000000000000000f (RPATH) Library rpath: [/usr/local/lib:/usr/local/lib/qt5]
0x000000000000001d (RUNPATH) Library runpath: [/usr/local/lib:/usr/local/lib/qt5]

Obtained from: AUR