Clean up fix for RegisterJobService

Prefer `each` to `find` since the former does the same thing
except doesn't add the extra delegation step that may be causing
the binding_of_caller gem issues.

Relates to https://gitlab.com/gitlab-org/gitlab-ce/issues/54281#note_119494004

app/services/ci/register_job_service.rb

@@ -36,7 +36,7 @@ module Ci
         builds = builds.with_any_tags
       end
 
-      selection = builds.find do |build|
+      builds.each do |build|
         next unless runner.can_pick?(build)
 
         begin
@@ -45,7 +45,7 @@ module Ci
           if assign_runner!(build, params)
             register_success(build)
 
-            break build
+            return Result.new(build, true)
           end
         rescue StateMachines::InvalidTransition, ActiveRecord::StaleObjectError
           # We are looping to find another build that is not conflicting
@@ -61,8 +61,6 @@ module Ci
         end
       end
 
-      return Result.new(selection, true) if selection
-
       register_failure
       Result.new(nil, valid)
     end