refs #45456, move drush installation to container start script

Author: jimyhuang

Dockerfile

@@ -51,7 +51,6 @@ RUN \
 
 RUN \
   curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer && \
-  composer global require drush/drush:8.4.12 && \
   cd /root/.composer && \
   find . | grep .git | xargs rm -rf && \
   composer clearcache