Remove unnecessary uniq calls

The code `where(id: ids)` is equivalent to `where(id: ids.uniq)`.

Since Rails 5 uses `distinct` instead of `uniq` and in most cases where
we use `uniq` with `pluck` we should simply remove the `uniq` call (as
done in this commit), we're also removing the `Rails/UniqBeforePluck`
rubocop rule.

.rubocop.yml

@@ -93,9 +93,6 @@ Rails/SaveBang:
 Rails/SkipsModelValidations:
   Enabled: true
 
-Rails/UniqBeforePluck:
-  Enabled: true
-
 RSpec/AlignLeftLetBrace:
   Enabled: false
 

app/controllers/concerns/moderate_actions.rb

@@ -25,7 +25,7 @@ module ModerateActions
       @resources.accessible_by(current_ability, :ignore_flag).each(&:ignore_flag)
 
     elsif params[:block_authors].present?
-      author_ids = @resources.pluck(author_id).uniq
+      author_ids = @resources.pluck(author_id)
       User.where(id: author_ids).accessible_by(current_ability, :block).each { |user| block_user user }
     end
 

app/controllers/tracking/budget_investments_controller.rb

@@ -48,7 +48,7 @@ class Tracking::BudgetInvestmentsController < Tracking::BaseController
 
     def heading_filters
       investments = @budget.investments.by_tracker(current_user.tracker&.id).distinct
-      investment_headings = Budget::Heading.where(id: investments.pluck(:heading_id).uniq)
+      investment_headings = Budget::Heading.where(id: investments.pluck(:heading_id))
                                            .order(name: :asc)
       all_headings_filter = [
                               {

lib/user_segments.rb

@@ -18,29 +18,29 @@ class UserSegments
   end
 
   def self.all_proposal_authors
-    author_ids(Proposal.pluck(:author_id).uniq)
+    author_ids(Proposal.pluck(:author_id))
   end
 
   def self.proposal_authors
-    author_ids(Proposal.not_archived.not_retired.pluck(:author_id).uniq)
+    author_ids(Proposal.not_archived.not_retired.pluck(:author_id))
   end
 
   def self.investment_authors
-    author_ids(current_budget_investments.pluck(:author_id).uniq)
+    author_ids(current_budget_investments.pluck(:author_id))
   end
 
   def self.feasible_and_undecided_investment_authors
     unfeasible_and_finished_condition = "feasibility = 'unfeasible' and valuation_finished = true"
     investments = current_budget_investments.where.not(unfeasible_and_finished_condition)
-    author_ids(investments.pluck(:author_id).uniq)
+    author_ids(investments.pluck(:author_id))
   end
 
   def self.selected_investment_authors
-    author_ids(current_budget_investments.selected.pluck(:author_id).uniq)
+    author_ids(current_budget_investments.selected.pluck(:author_id))
   end
 
   def self.winner_investment_authors
-    author_ids(current_budget_investments.winners.pluck(:author_id).uniq)
+    author_ids(current_budget_investments.winners.pluck(:author_id))
   end
 
   def self.not_supported_on_current_budget