refactor!: remove unused update-assets-dev.sh (#31810)

The file was introduced as part of the "decentralized devstack" spike.
We wanted a working Dockerfile in the edx-platform root,
and we wanted to speed it up by not relying on Paver.

edx-platform now has a working Dockerfile, and it does not use this script.

The paver-free-assets initiative is being continued here:
#31798
It will result in a new, prod-ready asset building script.