packetizer: copy: remove one bogus block delay/length computation
There's no reason to delay output to set block length.
- setting length is sout mux/access's job
- did not properly compute length regarding discontinuities or provided length
Probably need to discard pts == dts as well.
- never outputs last block until input drain (core issue)
- implies it also never outputs when sample count == 1 (refs #27393 (closed))