Remove the object pools feature flag

The flag defaulted to true, so there's no change unless users turned it
off. Given there's a lack of issues regarding object pools, this should
be OK.

app/models/project.rb

@@ -2175,8 +2175,7 @@ class Project < ApplicationRecord
     hashed_storage?(:repository) &&
       public? &&
       repository_exists? &&
-      Gitlab::CurrentSettings.hashed_storage_enabled &&
-      Feature.enabled?(:object_pools, self, default_enabled: true)
+      Gitlab::CurrentSettings.hashed_storage_enabled
   end
 
   def leave_pool_repository

doc/administration/repository_storage_types.md

@@ -82,19 +82,17 @@ by another folder with the next 2 characters. They are both stored in a special
 
 > [Introduced](https://gitlab.com/gitlab-org/gitaly/issues/1606) in GitLab 12.1.
 
-Forks of public projects are deduplicated by creating a third repository, the object pool, containing the objects from the source project. Using `objects/info/alternates`, the source project and forks use the object pool for shared objects. Objects are moved from the source project to the object pool when housekeeping is run on the source project.
+Forks of public projects are deduplicated by creating a third repository, the
+object pool, containing the objects from the source project. Using
+`objects/info/alternates`, the source project and forks use the object pool for
+shared objects. Objects are moved from the source project to the object pool
+when housekeeping is run on the source project.
 
 ```ruby
 # object pool paths
 "@pools/#{hash[0..1]}/#{hash[2..3]}/#{hash}.git"
 ```
 
-Object pools can be disabled using the `object_pools` feature flag, and can be
-disabled for individual projects by executing
-`Feature.disable(:object_pools, Project.find(<id>))`. Disabling object pools
-will not change existing deduplicated forks, but will prevent new forks from
-being deduplicated.
-
 DANGER: **Danger:**
 Do not run `git prune` or `git gc` in pool repositories! This can
 cause data loss in "real" repositories that depend on the pool in

doc/development/git_object_deduplication.md

@@ -8,30 +8,6 @@ storage disk use. To counteract this problem, we are adding Git object
 deduplication for forks to GitLab. In this document, we will describe how
 GitLab implements Git object deduplication.
 
-## Enabling Git object deduplication via feature flags
-
-As of GitLab 12.0, Git object deduplication in GitLab is still behind a
-feature flag. In this document, you can read about the effects of
-enabling the feature. Also, note that Git object deduplication is
-limited to forks of public projects on hashed repository storage.
-
-You can enable deduplication globally by setting the `object_pools`
-feature flag to `true`:
-
-``` {.ruby}
-Feature.enable(:object_pools)
-```
-
-Or just for forks of a specific project:
-
-``` {.ruby}
-fork_parent = Project.find(MY_PROJECT_ID)
-Feature.enable(:object_pools, fork_parent)
-```
-
-To check if a project uses Git object deduplication, look in a Rails
-console if `project.pool_repository` is present.
-
 ## Pool repositories
 
 ### Understanding Git alternates

spec/models/project_spec.rb

@@ -4877,35 +4877,22 @@ describe Project do
 
   describe '#git_objects_poolable?' do
     subject { project }
-
-    context 'when the feature flag is turned off' do
-      before do
-        stub_feature_flags(object_pools: false)
-      end
-
-      let(:project) { create(:project, :repository, :public) }
+    context 'when not using hashed storage' do
+      let(:project) { create(:project, :legacy_storage, :public, :repository) }
 
       it { is_expected.not_to be_git_objects_poolable }
     end
 
-    context 'when the feature flag is enabled' do
-      context 'when not using hashed storage' do
-        let(:project) { create(:project, :legacy_storage, :public, :repository) }
-
-        it { is_expected.not_to be_git_objects_poolable }
-      end
+    context 'when the project is not public' do
+      let(:project) { create(:project, :private) }
 
-      context 'when the project is not public' do
-        let(:project) { create(:project, :private) }
-
-        it { is_expected.not_to be_git_objects_poolable }
-      end
+      it { is_expected.not_to be_git_objects_poolable }
+    end
 
-      context 'when objects are poolable' do
-        let(:project) { create(:project, :repository, :public) }
+    context 'when objects are poolable' do
+      let(:project) { create(:project, :repository, :public) }
 
-        it { is_expected.to be_git_objects_poolable }
-      end
+      it { is_expected.to be_git_objects_poolable }
     end
   end