Remove hardcoded created_by user from returns methods

This applies only to some deprecated blocks and does not
change the new, working logic.

This means that if those methods were used by some store or
extension, they will now don't have the creator set instead
of having a specific user that could even be not present in the
database, causing the creator to be nil anyway.

core/app/models/spree/order_cancellations.rb

@@ -98,7 +98,6 @@ def cancel_unit(inventory_unit, reason: Spree::UnitCancel::DEFAULT_REASON, whodu
   # @return [Reimbursement] the reimbursement for inventory being canceled
   def reimburse_units(inventory_units, created_by: nil)
     unless created_by
-      created_by = Spree.user_class.find_by(email: 'spree@example.com')
       Spree::Deprecation.warn("Calling #reimburse_units on #{self} without created_by is deprecated")
     end
     reimbursement = nil

core/app/models/spree/reimbursement.rb

@@ -100,7 +100,6 @@ def unpaid_amount
 
     def perform!(created_by: nil)
       unless created_by
-        created_by = Spree.user_class.find_by(email: 'spree@example.com')
         Spree::Deprecation.warn("Calling #perform on #{self} without created_by is deprecated")
       end
       reimbursement_tax_calculator.call(self)
@@ -122,7 +121,6 @@ def perform!(created_by: nil)
 
     def simulate(created_by: nil)
       unless created_by
-        created_by = Spree.user_class.find_by(email: 'spree@example.com')
         Spree::Deprecation.warn("Calling #simulate on #{self} without created_by is deprecated")
       end
       reimbursement_simulator_tax_calculator.call(self)
@@ -151,7 +149,6 @@ def all_exchanges?
     # @return [void]
     def return_all(created_by: nil)
       unless created_by
-        created_by = Spree.user_class.find_by(email: 'spree@example.com')
         Spree::Deprecation.warn("Calling #return_all on #{self} without created_by is deprecated")
       end
       return_items.each(&:accept!)

core/app/models/spree/reimbursement_performer.rb

@@ -13,7 +13,6 @@ class << self
       # so they can be displayed in the Admin UI appropriately.
       def simulate(reimbursement, created_by: nil)
         unless created_by
-          created_by = Spree.user_class.find_by(email: 'spree@example.com')
           Spree::Deprecation.warn("Calling #simulate on #{self} without created_by is deprecated")
         end
         execute(reimbursement, true, created_by: created_by)
@@ -22,7 +21,6 @@ def simulate(reimbursement, created_by: nil)
       # Actually perform the reimbursement
       def perform(reimbursement, created_by: nil)
         unless created_by
-          created_by = Spree.user_class.find_by(email: 'spree@example.com')
           Spree::Deprecation.warn("Calling #perform on #{self} without created_by is deprecated")
         end
         execute(reimbursement, false, created_by: created_by)

core/app/models/spree/reimbursement_type/credit.rb

@@ -7,7 +7,6 @@ class ReimbursementType::Credit < Spree::ReimbursementType
     class << self
       def reimburse(reimbursement, return_items, simulate, created_by: nil)
         unless created_by
-          created_by = Spree.user_class.find_by(email: 'spree@example.com')
           Spree::Deprecation.warn("Calling #reimburse on #{self} without created_by is deprecated")
         end
         unpaid_amount = return_items.sum(&:total).round(2, :down)

core/app/models/spree/reimbursement_type/store_credit.rb

@@ -6,7 +6,6 @@ class Spree::ReimbursementType::StoreCredit < Spree::ReimbursementType
   class << self
     def reimburse(reimbursement, return_items, simulate, created_by: nil)
       unless created_by
-        created_by = Spree.user_class.find_by(email: 'spree@example.com')
         Spree::Deprecation.warn("Calling #reimburse on #{self} without created_by is deprecated")
       end
       unpaid_amount = return_items.sum(&:total).to_d.round(2, :down)