zoom-us: fix launch (#80005)

zoom-us: fix launch

Probably due to glibc update, ZoomLauncher became broken when v4l is present in
LD_PRELOAD path. It can be fixed by a) removing ZoomLauncher from startup chain,
so `zoom` is started directly or b) removing v4l from LD_PRELOAD.

The reason v4l was added before was because my video was rotated upside down without it.
Seem like nowadays this is fixed by Zoom itself, so I'm removing it.

Fixes https://github.com/NixOS/nixpkgs/issues/79954

Co-authored-by: @mmlb