[docker] remove `codelab_otsim` Dockerfile (#7396)

* Delete obsolete codelab_otsim Dockerfile
* Remove codelab_otsim from git Docker Action

.github/workflows/docker.yml

@@ -47,7 +47,6 @@ jobs:
       matrix:
         include:
           - docker_name: environment
-          - docker_name: codelab_otsim
     steps:
     - uses: actions/checkout@v2
       with:

etc/docker/codelab_otsim/Dockerfile

@@ -1,30 +0,0 @@
-# Ubuntu image with tools required to build OpenThread
-FROM ubuntu:18.04
-
-ENV DEBIAN_FRONTEND noninteractive
-ARG OT_GIT_REF=main
-
-# Install dependencies:
-RUN apt-get update -qq
-
-# Install packages needed for build and runtime:
-RUN apt-get --no-install-recommends install -y \
-    git \
-    sudo \
-    inetutils-ping \
-    software-properties-common \
-    ca-certificates \
-    && update-ca-certificates
-
-# Install OpenThread
-RUN mkdir -p ~/src/openthread && \
-    cd ~/src/openthread && \
-    git init . && \
-    git fetch https://github.com/openthread/openthread.git ${OT_GIT_REF} && \
-    git checkout FETCH_HEAD && \
-    ./script/bootstrap && \
-    ./bootstrap && \
-    make -f examples/Makefile-simulation
-
-# Install OpenThread Daemon and ot-ctl
-RUN cd ~/src/openthread && make -f src/posix/Makefile-posix DAEMON=1