INSTALL.sh: Remove old MDIS sources directory
requested to merge 336-install-sh-does-not-remove-previous-mdis-sources-installation-even-when-the-user-requests-for-it into mad-dev
The script INSTALL.sh was prepared to remove the old MDIS sources directory, however, the script was not actually removing it.
Now, the script will remove such directory if the user requests it.
Closes #336 (closed)