Remove forgotten LinuxMint occurrence

Right now we don't officialy support LinuxMint as our
documentation says [1], it seems LinuxMint is a relict
and got forgotten over time.

This patch removes LinuxMint from the code in order not to
confuse users.

[1] https://docs.openstack.org/devstack/latest/
Closes-Bug: #1983427

Change-Id: Ie1ced25f89389494b28a7b2e9bb1c4273e002dd5

Author: kopecmartin

doc/source/plugins.rst

@@ -238,7 +238,7 @@ package dependencies, packages may be listed at the following
 locations in the top-level of the plugin repository:
 
 - ``./devstack/files/debs/$plugin_name`` - Packages to install when running
-  on Ubuntu, Debian or Linux Mint.
+  on Ubuntu or Debian.
 
 - ``./devstack/files/rpms/$plugin_name`` - Packages to install when running
   on Red Hat, Fedora, or CentOS.

functions-common

@@ -426,7 +426,7 @@ function GetOSVersion {
         os_VENDOR=$(lsb_release -i -s)
     fi
 
-    if [[ $os_VENDOR =~ (Debian|Ubuntu|LinuxMint) ]]; then
+    if [[ $os_VENDOR =~ (Debian|Ubuntu) ]]; then
         os_PACKAGE="deb"
     else
         os_PACKAGE="rpm"
@@ -444,9 +444,8 @@ declare -g DISTRO
 
 function GetDistro {
     GetOSVersion
-    if [[ "$os_VENDOR" =~ (Ubuntu) || "$os_VENDOR" =~ (Debian) || \
-            "$os_VENDOR" =~ (LinuxMint) ]]; then
-        # 'Everyone' refers to Ubuntu / Debian / Mint releases by
+    if [[ "$os_VENDOR" =~ (Ubuntu) || "$os_VENDOR" =~ (Debian) ]]; then
+        # 'Everyone' refers to Ubuntu / Debian releases by
         # the code name adjective
         DISTRO=$os_CODENAME
     elif [[ "$os_VENDOR" =~ (Fedora) ]]; then