Remove unneeded docker steps

Dockerfile

@@ -21,15 +21,3 @@ RUN chown builduser:builduser /tmp/workspace
 
 USER builduser
 WORKDIR /home/builduser
-
-# Prime the LIBCHROMIUMCONTENT_GIT_CACHE and src dirs
-RUN mkdir /tmp/libcc_cache
-RUN chown builduser:builduser /tmp/libcc_cache
-RUN git clone https://github.com/electron/libchromiumcontent.git project
-WORKDIR /home/builduser/project
-RUN git checkout circleci_test
-RUN script/bootstrap
-RUN export LIBCHROMIUMCONTENT_GIT_CACHE=/tmp/libcc_cache
-RUN script/update --source_only
-
-WORKDIR /home/builduser