Make DraftVaccinationRecord#performed_at_time optional

This is causing an issue in the already vaccinated flow. It should not
be necessary to enter a time, only a date to specify when a previous vaccination
was performed.

Jira-Issue: MAV-2848

Author: stevehook

app/models/draft_vaccination_record.rb

@@ -86,9 +86,6 @@ def wizard_steps
 
   on_wizard_step :date_and_time, exact: true do
     validates :performed_at_date, presence: true
-    validates :performed_at_time,
-              presence: true,
-              unless: :national_reporting_user_and_record?
     validate :performed_at_date_within_range
   end
 

spec/features/mmr_already_had_spec.rb

@@ -212,8 +212,6 @@ def when_i_fill_in_the_date_and_continue
     fill_in "Day", with: @vaccination_date.day
     fill_in "Month", with: @vaccination_date.month
     fill_in "Year", with: @vaccination_date.year
-    fill_in "Hour", with: "12"
-    fill_in "Minute", with: "00"
     click_on "Continue"
   end