community/heimdall: upgrade to 2.1.0

And deprecate heimdall_wait_for_device.sh. Heimdall 2.1.0 has a new
option --wait which can be used instead of running
heimdall_wait_for_device.sh separately.

For full changelog, see
https://git.sr.ht/~grimler/Heimdall/refs/v2.1.0