Cleanup checks for replication slot in Geo

This removes checking for the presence of PG
replication slots. This is not necessary anymore since that has been
supported since PG 9.4 and we're on >= PG11 now.

ee/app/models/geo_node.rb

@@ -300,19 +300,19 @@ class GeoNode < ApplicationRecord
   end
 
   def replication_slots_count
-    return unless Gitlab::Database.replication_slots_supported? && primary?
+    return unless primary?
 
     PgReplicationSlot.count
   end
 
   def replication_slots_used_count
-    return unless Gitlab::Database.replication_slots_supported? && primary?
+    return unless primary?
 
     PgReplicationSlot.used_slots_count
   end
 
   def replication_slots_max_retained_wal_bytes
-    return unless Gitlab::Database.replication_slots_supported? && primary?
+    return unless primary?
 
     PgReplicationSlot.max_retained_wal
   end

ee/spec/models/pg_replication_slot_spec.rb

@@ -3,8 +3,6 @@
 require 'spec_helper'
 
 RSpec.describe PgReplicationSlot do
-  if Gitlab::Database.replication_slots_supported?
-    describe 'with replication slot support' do
   it '#max_replication_slots' do
     expect(described_class.max_replication_slots).to be >= 0
   end
@@ -49,6 +47,4 @@ RSpec.describe PgReplicationSlot do
       expect(slot['retained_bytes']).to be_nil
     end
   end
-    end
-  end
 end

lib/gitlab/database.rb

@@ -99,10 +99,6 @@ module Gitlab
       version.to_f < 10
     end
 
-    def self.replication_slots_supported?
-      version.to_f >= 9.4
-    end
-
     def self.postgresql_minimum_supported_version?
       version.to_f >= MINIMUM_POSTGRES_VERSION
     end

spec/lib/gitlab/database_spec.rb

@@ -156,20 +156,6 @@ RSpec.describe Gitlab::Database do
     end
   end
 
-  describe '.replication_slots_supported?' do
-    it 'returns false when using PostgreSQL 9.3' do
-      allow(described_class).to receive(:version).and_return('9.3.1')
-
-      expect(described_class.replication_slots_supported?).to eq(false)
-    end
-
-    it 'returns true when using PostgreSQL 9.4.0 or newer' do
-      allow(described_class).to receive(:version).and_return('9.4.0')
-
-      expect(described_class.replication_slots_supported?).to eq(true)
-    end
-  end
-
   describe '.pg_wal_lsn_diff' do
     it 'returns old name when using PostgreSQL 9.6' do
       allow(described_class).to receive(:version).and_return('9.6')