Remove outdated instructions for Linux Mint.

The Linux Mint instructions were still referring to steps in the Ubuntu
and Debian instructions that do not exist in this version of the docs.
Signed-off-by: fhoekstra <[email protected]>

Author: fhoekstra

docs/installation.md

@@ -173,8 +173,6 @@ sudo apt-get -y install podman
 
 Follow the steps for Ubuntu (or Debian if you use LMDE).
 
-Replace `$(lsb_release -rs)` with `$(grep DISTRIB_RELEASE= /etc/upstream-release/lsb-release | cut -d "=" -f 2)` for Ubuntu steps.
-
 ### Installing development versions of Podman
 
 #### [Fedora](https://getfedora.org)