Simplify health check and spec

lib/gitlab/geo/health_check.rb

@@ -55,8 +55,6 @@ module Gitlab
       end
 
       def self.database_secondary?
-        raise NotImplementedError unless Gitlab::Database.postgresql?
-
         ActiveRecord::Base.connection.execute('SELECT pg_is_in_recovery()')
           .first
           .fetch('pg_is_in_recovery') == 't'
@@ -64,8 +62,6 @@ module Gitlab
 
       def self.db_replication_lag
         # Obtain the replication lag in seconds
-        raise NotImplementedError unless Gitlab::Database.postgresql?
-
         ActiveRecord::Base.connection.execute('
           SELECT CASE
                  WHEN pg_last_xlog_receive_location() = pg_last_xlog_replay_location()

spec/lib/gitlab/geo/health_check_spec.rb

@@ -30,7 +30,7 @@ describe Gitlab::Geo::HealthCheck, :postgresql do
       allow(Gitlab::Geo).to receive(:secondary?) { true }
       allow(Gitlab::Geo).to receive(:configured?) { true }
       allow(Gitlab::Database).to receive(:postgresql?) { true }
-      allow(ActiveRecord::Base).to receive_message_chain(:connection, :execute, :first, :fetch) { 'f' }
+      allow(described_class).to receive(:database_secondary?) { false }
 
       expect(subject.perform_checks).not_to be_blank
     end
@@ -39,7 +39,7 @@ describe Gitlab::Geo::HealthCheck, :postgresql do
       allow(Gitlab::Geo).to receive(:secondary?) { true }
       allow(Gitlab::Geo).to receive(:configured?) { true }
       allow(Gitlab::Database).to receive(:postgresql?) { true }
-      allow(ActiveRecord::Base).to receive_message_chain(:connection, :execute, :first, :fetch) { 'f' }
+      allow(described_class).to receive(:database_secondary?) { false }
 
       expect(subject.perform_checks).to include('not configured for streaming replication')
     end