Remove unnecessary includes of ShellAdapter

Determined by running the script:

```
included = `git grep --name-only ShellAdapter`.chomp.split("\n")
used = `git grep --name-only gitlab_shell`.chomp.split("\n")
included - used
```

app/models/concerns/storage/legacy_namespace.rb

@@ -4,6 +4,8 @@ module Storage
   module LegacyNamespace
     extend ActiveSupport::Concern
 
+    include Gitlab::ShellAdapter
+
     def move_dir
       proj_with_tags = first_project_with_container_registry_tags
 

app/models/members/project_member.rb

@@ -3,8 +3,6 @@
 class ProjectMember < Member
   SOURCE_TYPE = 'Project'.freeze
 
-  include Gitlab::ShellAdapter
-
   belongs_to :project, foreign_key: 'source_id'
 
   # Make sure project member points only to project as it source

app/models/namespace.rb

@@ -3,7 +3,6 @@
 class Namespace < ActiveRecord::Base
   include CacheMarkdownField
   include Sortable
-  include Gitlab::ShellAdapter
   include Gitlab::VisibilityLevel
   include Routable
   include AfterCommitQueue

app/models/protected_branch.rb

 # frozen_string_literal: true
 
 class ProtectedBranch < ActiveRecord::Base
-  include Gitlab::ShellAdapter
   include ProtectedRef
 
   protected_ref_access_levels :merge, :push

app/models/protected_tag.rb

 # frozen_string_literal: true
 
 class ProtectedTag < ActiveRecord::Base
-  include Gitlab::ShellAdapter
   include ProtectedRef
 
   validates :name, uniqueness: { scope: :project_id }

app/models/repository.rb

@@ -17,7 +17,6 @@ class Repository
     #{REF_ENVIRONMENTS}
   ].freeze
 
-  include Gitlab::ShellAdapter
   include Gitlab::RepositoryCacheAdapter
 
   attr_accessor :full_path, :disk_path, :project, :is_wiki

app/workers/repository_update_remote_mirror_worker.rb

@@ -5,7 +5,6 @@ class RepositoryUpdateRemoteMirrorWorker
   UpdateError = Class.new(StandardError)
 
   include ApplicationWorker
-  include Gitlab::ShellAdapter
 
   sidekiq_options retry: 3, dead: false
 

db/post_migrate/20161221153951_rename_reserved_project_names.rb

 class RenameReservedProjectNames < ActiveRecord::Migration[4.2]
   include Gitlab::Database::MigrationHelpers
-  include Gitlab::ShellAdapter
 
   DOWNTIME = false
 

db/post_migrate/20170313133418_rename_more_reserved_project_names.rb

 class RenameMoreReservedProjectNames < ActiveRecord::Migration[4.2]
   include Gitlab::Database::MigrationHelpers
-  include Gitlab::ShellAdapter
 
   DOWNTIME = false
 

lib/gitlab/bitbucket_server_import/importer.rb

@@ -3,8 +3,6 @@
 module Gitlab
   module BitbucketServerImport
     class Importer
-      include Gitlab::ShellAdapter
-
       attr_reader :recover_missing_commits
       attr_reader :project, :project_key, :repository_slug, :client, :errors, :users
       attr_accessor :logger

lib/gitlab/import_export/repo_restorer.rb

@@ -4,7 +4,6 @@ module Gitlab
   module ImportExport
     class RepoRestorer
       include Gitlab::ImportExport::CommandLineUtil
-      include Gitlab::ShellAdapter
 
       def initialize(project:, shared:, path_to_bundle:)
         @project = project

spec/models/members/project_member_spec.rb

@@ -11,10 +11,6 @@ describe ProjectMember do
     it { is_expected.to validate_inclusion_of(:access_level).in_array(Gitlab::Access.values) }
   end
 
-  describe 'modules' do
-    it { is_expected.to include_module(Gitlab::ShellAdapter) }
-  end
-
   describe '.access_level_roles' do
     it 'returns Gitlab::Access.options' do
       expect(described_class.access_level_roles).to eq(Gitlab::Access.options)