FIX: Move selectable_avatars_mode_validator_spec to new directory (#16048)

Lib specs moved in 45cc16098dee51fc2bee0e5873afa51fe2bd1ea3
Move the new selectable_avatars_mode_validator_spec to the new location
Remove the old selectable_avatars_enabled_validator_spec

follow-up of d1bdb6c65d1d1de8f610d1e39bf3788c0c241ef6

spec/lib/validators/selectable_avatars_enabled_validator_spec.rb

@@ -1,30 +0,0 @@
-# frozen_string_literal: true
-
-require 'rails_helper'
-
-describe SelectableAvatarsEnabledValidator do
-  describe '#valid_value?' do
-    subject(:validator) { described_class.new }
-
-    it "returns true when disabling" do
-      SiteSetting.selectable_avatars = ""
-      expect(validator.valid_value?("f")).to eq(true)
-
-      SiteSetting.selectable_avatars = [Fabricate(:image_upload), Fabricate(:image_upload)]
-      expect(validator.valid_value?("f")).to eq(true)
-    end
-
-    it "returns true when there are at least two selectable avatars" do
-      SiteSetting.selectable_avatars = [Fabricate(:image_upload), Fabricate(:image_upload)]
-      expect(validator.valid_value?("t")).to eq(true)
-    end
-
-    it "returns false when selectable avatars is blank or has one avatar" do
-      SiteSetting.selectable_avatars = ""
-      expect(validator.valid_value?("t")).to eq(false)
-
-      SiteSetting.selectable_avatars = [Fabricate(:image_upload)]
-      expect(validator.valid_value?("t")).to eq(false)
-    end
-  end
-end