[Bug] r.viewshed does not clean tempfiles

[ninsbl]

Describe the bug After running r.viewshed, temporary files remain in the .tmp directory.

To Reproduce

ls ${LOCATION}/.tmp/*
g.region raster=elevation.10m
r.viewshed input=elevation.10m output=viewshed coordinates=598869,4916642 memory=800
ls ${LOCATION}/.tmp/*

Expected behavior Temporary files in .tmp are removed when process finishes.

System description (please complete the following information):

• Operating System: Ubuntu 18.04.1 LTS
• GRASS GIS 7.8.3

Additional context Remaining tempfiles can slow down closing of GRASS GIS.

[neteler]

(probably the same applies to r.terraflow)