Remove proxy config in .gitlab-ci.yml

Current runners are not allowed to used this internal proxy. And it shouldn't be there anyway.

(Will remove the WIP once the new runner works)

.gitlab-ci.yml

@@ -2,8 +2,6 @@ image: elixir:latest
 
 before_script:
   - |
-    export HTTP_PROXY="http://172.17.0.1:3128"
-    export HTTPS_PROXY="http://172.17.0.1:3128"
     apt-get update && apt-get install -y libsodium-dev
     mix local.rebar --force
     mix local.hex --force