Fix invalid code signature due to Sparkle Framework

This adds a missing rpath to the vlc-osx-static executable and removed install_name post-processing from the Sparkle framework in contribs, which would lead to invalidating the Sparkle ad-hoc signature needed on arm64 (Apple Silicon) Macs.

So this should fix the broken nightly builds on arm64 as reported in #26127 (closed)

Should be BPed to 3.x once merged.