This reverts commit 937e1c2e.

Notice that Elixir 1.12.0 requires Erlang/OTP 21 or higher
BTW, this workaround works only with rebar2... unfortunately
rebar3 doesn't compile the elixir files from lib/

However, to build a release with OTP 24 requires Elixir 1.11.4 or higher

Reference: https://ferd.ca/you-ve-got-to-upgrade-rebar3.html

mod_mix: Use disco identity conference/mix