Remove unused model

It was added in commit 74083df1; we're not sure why.

app/models/budget_rol_assignment.rb

@@ -1,4 +0,0 @@
-class BudgetRolAssignment < ApplicationRecord
-  belongs_to :budget
-  belongs_to :user
-end

app/models/user.rb

@@ -45,7 +45,6 @@ class User < ApplicationRecord
     inverse_of:  :receiver
   has_many :legislation_answers, class_name: "Legislation::Answer", dependent: :destroy, inverse_of: :user
   has_many :follows
-  has_many :budget_rol_assignments
   has_many :legislation_annotations,
     class_name:  "Legislation::Annotation",
     foreign_key: :author_id,
@@ -80,7 +79,6 @@ class User < ApplicationRecord
     foreign_key: :author_id,
     inverse_of:  :author
   has_many :topics, foreign_key: :author_id, inverse_of: :author
-  has_many :budgets, through: :budget_rol_assignments
   belongs_to :geozone
 
   validates :username, presence: true, if: :username_required?

db/migrate/20191031172132_drop_budget_rol_assignments.rb

@@ -0,0 +1,9 @@
+class DropBudgetRolAssignments < ActiveRecord::Migration[5.0]
+  def up
+    drop_table :budget_rol_assignments
+  end
+
+  def down
+    fail ActiveRecord::IrreversibleMigration
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20191030160347) do
+ActiveRecord::Schema.define(version: 20191031172132) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -340,16 +340,6 @@ ActiveRecord::Schema.define(version: 20191030160347) do
     t.datetime "updated_at",    null: false
   end
 
-  create_table "budget_rol_assignments", force: :cascade do |t|
-    t.integer  "budget_id"
-    t.integer  "user_id"
-    t.string   "rol"
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.index ["budget_id"], name: "index_budget_rol_assignments_on_budget_id", using: :btree
-    t.index ["user_id"], name: "index_budget_rol_assignments_on_user_id", using: :btree
-  end
-
   create_table "budget_tracker_assignments", force: :cascade do |t|
     t.integer  "tracker_id"
     t.integer  "investment_id"
@@ -1713,8 +1703,6 @@ ActiveRecord::Schema.define(version: 20191030160347) do
   add_foreign_key "budget_administrators", "administrators"
   add_foreign_key "budget_administrators", "budgets"
   add_foreign_key "budget_investments", "communities"
-  add_foreign_key "budget_rol_assignments", "budgets"
-  add_foreign_key "budget_rol_assignments", "users"
   add_foreign_key "budget_tracker_assignments", "trackers"
   add_foreign_key "budget_trackers", "budgets"
   add_foreign_key "budget_trackers", "trackers"