Use raw value of maximum_timeout for Runner registration API

lib/api/runner.rb

@@ -14,12 +14,11 @@ module API
         optional :locked, type: Boolean, desc: 'Should Runner be locked for current project'
         optional :run_untagged, type: Boolean, desc: 'Should Runner handle untagged jobs'
         optional :tag_list, type: Array[String], desc: %q(List of Runner's tags)
-        optional :maximum_timeout, type: String, desc: 'Maximum timeout set when this Runner will handle the job'
+        optional :maximum_timeout, type: Integer, desc: 'Maximum timeout set when this Runner will handle the job'
       end
       post '/' do
-        attributes = attributes_for_keys([:description, :locked, :run_untagged, :tag_list])
+        attributes = attributes_for_keys([:description, :locked, :run_untagged, :tag_list, :maximum_timeout])
           .merge(get_runner_details_from_request)
-          .merge(maximum_timeout_human_readable: params[:maximum_timeout])
 
         runner =
           if runner_registration_token_valid?

spec/requests/api/runner_spec.rb

@@ -112,7 +112,7 @@ describe API::Runner do
       context 'when maximum job timeout is specified' do
         it 'creates runner' do
           post api('/runners'), token: registration_token,
-                                maximum_timeout: '2h 30m'
+                                maximum_timeout: 9000
 
           expect(response).to have_gitlab_http_status 201
           expect(Ci::Runner.first.maximum_timeout).to eq(9000)