Remove obsolete mysql client install

This fails nowadays,and the client is already installed via the mysql
package in the first place.

site-cookbooks/backup/recipes/default.rb

@@ -62,12 +62,6 @@ cron "default backup model" do
 end
 
 include_recipe 'logrotate'
-# Install MySQL client (includes mysqldump)
-mysql_client 'default' do
-  action :create
-  version '5.7' if node[:platform_version].to_f == 18.04
-  not_if { node["backup"]["mysql"]["databases"].empty? }
-end
 
 # Write the credentials file to allow dumps without password for the root
 # user (https://dev.mysql.com/doc/refman/5.7/en/option-files.html)