Remove unused deployment configuration variables

The server_name variable isn't used since we removed the Apache task in
commit 012d5297e, db_server and config_files aren't used since we
removed the capistrano templates in that same commit, and full_app_name
isn't used since commit 94a7e13dc.

config/deploy.rb

@@ -10,10 +10,7 @@ set :rails_env, fetch(:stage)
 set :rvm1_map_bins, -> { fetch(:rvm_map_bins).to_a.concat(%w[rake gem bundle ruby]).uniq }
 
 set :application, "consul"
-set :full_app_name, deploysecret(:full_app_name)
 set :deploy_to, deploysecret(:deploy_to)
-set :server_name, deploysecret(:server_name)
-set :db_server, deploysecret(:db_server)
 set :ssh_options, port: deploysecret(:ssh_port)
 
 set :repo_url, "https://github.com/consul/consul.git"
@@ -36,12 +33,6 @@ set :puma_conf, "#{release_path}/config/puma/#{fetch(:rails_env)}.rb"
 set :delayed_job_workers, 2
 set :delayed_job_roles, :background
 
-set(:config_files, %w[
-  log_rotation
-  database.yml
-  secrets.yml
-])
-
 set :whenever_roles, -> { :app }
 
 namespace :deploy do