Use let in valuator group

This way we can remove a useless assignment without making the code
harder to read vertically.

spec/features/admin/valuator_groups_spec.rb

@@ -81,10 +81,10 @@ describe "Valuator groups" do
   end
 
   context "Assign valuators to groups" do
+    let(:valuator) { create(:valuator) }
 
     scenario "Add a valuator to a group" do
-      valuator = create(:valuator)
+      create(:valuator_group, name: "Health")
-      group = create(:valuator_group, name: "Health")
 
       visit edit_admin_valuator_path(valuator)
 
@@ -96,10 +96,8 @@ describe "Valuator groups" do
     end
 
     scenario "Update a valuator's group" do
-      valuator = create(:valuator)
+      valuator.update(valuator_group: create(:valuator_group, name: "Economy"))
-      group1 = create(:valuator_group, name: "Health")
+      create(:valuator_group, name: "Health")
-      group2 = create(:valuator_group, name: "Economy")
-      valuator.update(valuator_group: group1)
 
       visit edit_admin_valuator_path(valuator)
       select "Economy", from: "valuator_valuator_group_id"
@@ -110,9 +108,7 @@ describe "Valuator groups" do
     end
 
     scenario "Remove a valuator from a group" do
-      valuator = create(:valuator)
+      valuator.update(valuator_group: create(:valuator_group, name: "Health"))
-      group1 = create(:valuator_group, name: "Health")
-      valuator.update(valuator_group: group1)
 
       visit edit_admin_valuator_path(valuator)
       select "", from: "valuator_valuator_group_id"