When a package that is in the repos is relatively current. I recommend using the normal package management methods. Using the official repos or well maintained ppa's allows you to receive future updates with minimal effort. When the target system is air gapped, apt-offline is a viable method to manage packages.
Downloaded installers may or may not include uninstall scripts. If the software doesn't it can be difficult to properly remove all of the components. However you can manually uninstall by looking into the install script to find where the components were installed. If you are not familiar with the language of the installer, Perl in this case, mostly look at the comments.
In the case of the
install-tl in install-tl-unx.tar.gz. The comments on lines 1393-1401 list "Environment variables and default values on UNIX". The install dir is listed as
/usr/local/texlive. The user config files should be in
~/.texlive2017/, leaving them likely will not cause any issues.
rm -rf /usr/local/texlive should remove the program. Your
PATH variable may be altered to include
/usr/local/texlive, however that is just an informed guess.
# Environment variables and default values on UNIX:
# TEXLIVE_INSTALL_PREFIX /usr/local/texlive => $tex_prefix
# TEXLIVE_INSTALL_TEXDIR $tex_prefix/2010 => $TEXDIR
# TEXLIVE_INSTALL_TEXMFSYSVAR $TEXDIR/texmf-var
# TEXLIVE_INSTALL_TEXMFSYSCONFIG $TEXDIR/texmf-config
# TEXLIVE_INSTALL_TEXMFLOCAL $tex_prefix/texmf-local
# TEXLIVE_INSTALL_TEXMFHOME '$HOME/texmf'
# TEXLIVE_INSTALL_TEXMFVAR ~/.texlive2010/texmf-var
# TEXLIVE_INSTALL_TEXMFCONFIG ~/.texlive2010/texmf-config