[GRASS-git] [OSGeo/grass] 30c3b4: docker: update Ubuntu based images (#1180)

[Markus Neteler]

  Branch: refs/heads/releasebranch_7_8
  Home:   https://github.com/OSGeo/grass
  Commit: 30c3b4e886a6448e675d93088037e6890b165db0
      https://github.com/OSGeo/grass/commit/30c3b4e886a6448e675d93088037e6890b165db0
  Author: Markus Neteler <neteler at gmail.com>
  Date:   2020-12-16 (Wed, 16 Dec 2020)

  Changed paths:
    M docker/README.md
    R docker/ubuntu/Dockerfile_ubuntu_latest_pdal
    M docker/ubuntu/Dockerfile_ubuntu_pdal

  Log Message:
  -----------
  docker: update Ubuntu based images (#1180)

* docker: update Ubuntu based images

- update to ubuntu:20.04 base image
- cleanup potentially leftover GISRC file with wrong path to "demolocation"
- use PROJ from Ubuntu

* avoid hardcoded ARCH

* generalize .grassrc79 to .grassrc7?

* removed outdated Ubuntu19 docker image