Do not check for secondary? but use readonly? instead

See gitlab-org/gitlab-ee!2983.

app/services/keys/last_used_service.rb

 module Keys
   class LastUsedService
-    prepend ::EE::Keys::LastUsedService
-
     TIMEOUT = 1.day.to_i
 
     attr_reader :key
@@ -18,6 +16,8 @@ module Keys
     end
 
     def update?
+      return false if ::Gitlab::Database.readonly?
+
       last_used = key.last_used_at
 
       return false if last_used && (Time.zone.now - last_used) <= TIMEOUT

ee/app/services/ee/keys/last_used_service.rb

-module EE
-  module Keys
-    module LastUsedService
-      def update?
-        raise NotImplementedError unless defined?(super)
-
-        !::Gitlab::Geo.secondary? && super
-      end
-    end
-  end
-end

spec/ee/spec/services/ee/keys/last_used_service_spec.rb

 require 'spec_helper'
 
 describe Keys::LastUsedService do
-  it 'does not run on Geo secondaries', :clean_gitlab_redis_shared_state do
+  it 'does not run on read-only GitLab instances', :clean_gitlab_redis_shared_state do
     key = create(:key, last_used_at: 1.year.ago)
     original_time = key.last_used_at
 
-    allow(::Gitlab::Geo).to receive(:secondary?).and_return(true)
+    allow(::Gitlab::Database).to receive(:readonly?).and_return(true)
     described_class.new(key).execute
 
     expect(key.reload.last_used_at).to be_like_time(original_time)