More cleanup for ubuntu-18.04 image

ubuntu-18.04/Dockerfile

@@ -24,6 +24,9 @@ RUN set -x \
     && echo extension=mcrypt.so > /etc/php/7.2/cli/conf.d/20-mcrypt.ini \
     && echo extension=pdo_sqlsrv.so > /etc/php/7.2/cli/conf.d/30-pdo_sqlsrv.ini \
     && echo extension=sqlsrv.so > /etc/php/7.2/cli/conf.d/20-sqlsrv.ini \
+    # uninstall all headers and libraries
+    && apt-get purge -y -f --force-yes \
+       php7.2-dev php-pear build-essential unixodbc-dev \
     # perform image cleanup.
     && docker-run-bootstrap \
     && docker-image-cleanup