Remove deny disk access feature flag

Introduced in 189342fc, its not clear
why. This feature flag hasn't been used
d505f2a8, which is a year before it got
introduced.

config/feature_flags/development/gitaly_deny_disk_access.yml

----
-name: gitaly_deny_disk_access
-introduced_by_url: 
-rollout_issue_url: 
-milestone: 
-type: development
-group: 
-default_enabled: false

lib/gitlab/gitaly_client/storage_settings.rb

@@ -23,7 +23,6 @@ module Gitlab
 
       MUTEX = Mutex.new
 
-      DISK_ACCESS_DENIED_FLAG = :deny_disk_access
       ALLOW_KEY = :allow_disk_access
 
       # If your code needs this method then your code needs to be fixed.
@@ -34,7 +33,7 @@ module Gitlab
       def self.disk_access_denied?
         return false if rugged_enabled?
 
-        !temporarily_allowed?(ALLOW_KEY) && Feature::Gitaly.enabled?(DISK_ACCESS_DENIED_FLAG)
+        !temporarily_allowed?(ALLOW_KEY)
       rescue
         false # Err on the side of caution, don't break gitlab for people
       end
@@ -62,7 +61,7 @@ module Gitlab
 
       def legacy_disk_path
         if self.class.disk_access_denied?
-          raise DirectPathAccessError, "git disk access denied via the gitaly_#{DISK_ACCESS_DENIED_FLAG} feature"
+          raise DirectPathAccessError, "git disk access denied"
         end
 
         @legacy_disk_path

spec/support/helpers/seed_helper.rb

@@ -4,7 +4,7 @@ require_relative 'test_env'
 
 # This file is specific to specs in spec/lib/gitlab/git/
 
-SEED_STORAGE_PATH      = TestEnv.repos_path
+SEED_STORAGE_PATH      = Gitlab::GitalyClient::StorageSettings.allow_disk_access { TestEnv.repos_path }
 TEST_REPO_PATH         = 'gitlab-git-test.git'
 TEST_NORMAL_REPO_PATH  = 'not-bare-repo.git'
 TEST_MUTABLE_REPO_PATH = 'mutable-repo.git'

spec/support/helpers/test_env.rb

@@ -149,7 +149,9 @@ module TestEnv
       end
     end
 
-    FileUtils.mkdir_p(repos_path)
+    FileUtils.mkdir_p(
+      Gitlab::GitalyClient::StorageSettings.allow_disk_access { TestEnv.repos_path }
+    )
     FileUtils.mkdir_p(SECOND_STORAGE_PATH)
     FileUtils.mkdir_p(backup_path)
     FileUtils.mkdir_p(pages_path)