[Bug] g.gui.iclass uses deprecated mlab function

[CarlosGrohmann]

Description
I'm running 7.9 (from github) in Linux Manjaro. Matplotlib is installed and I use it elsewhere. Python 3.8.2.
When trying to run g.gui.iclass, I got the warning "unable needed to import packages for scatter plot". The error reported is that it can't import "dist_point_to_segment". From what I found, this function was deprecated in recent versions of matplotlib. See here: ESMG/pyroms#18

To Reproduce
Click on wxgui menu "Imagery - Classify Image - interactive input for supervised classification"

Expected behavior
I expected the tool to open without issues, as I have matplotlib working

Screenshots

**System description **

• Operating System: Linux Manjaro
• GRASS GIS version 7.9.dev

version=7.9.dev
date=2020
revision=ad079931e
build_date=2020-05-04
build_platform=x86_64-pc-linux-gnu
build_off_t_size=8
libgis_revision=f89b009b5
libgis_date=2020-04-24T11:32:32+00:00
proj=6.3.1
gdal=3.0.4
geos=3.8.0
sqlite=3.31.1

Additional context
Add any other context about the problem here.

[nilason]

This is duplicate of #461. May be closed as such.