macOS Support: drop decord

[AmitMY]

AToken uses decord for data processing.
However, it is not well supported on macOS, with python > 3.8

The problem is that apparently decord is built and published for Mac only up to python 3.8 (see master/.github/workflows/pypi.yml).

pip install decord gives

ERROR: Could not find a version that satisfies the requirement decord (from versions: none)
ERROR: No matching distribution found for decord

[jiasenlu]

on mac you can install eval-decord

pip install eva-decord

However, our current code only support with flash attention, which not supported by macOS yet.