Remove unused `model_have_error_on_field` matcher (#33273)

spec/models/form/import_spec.rb

@@ -61,10 +61,7 @@ RSpec.describe Form::Import do
       let(:import_type) { 'following' }
       let(:import_file) { 'boop.ogg' }
 
-      it 'has errors' do
+      it { is_expected.to_not allow_value(data).for(:data) }
-        # NOTE: not testing more specific error because we don't know the string to match
-        expect(subject).to model_have_error_on_field(:data)
-      end
     end
 
     context 'when importing more follows than allowed' do

spec/support/matchers/model/model_have_error_on_field.rb

@@ -1,15 +0,0 @@
-# frozen_string_literal: true
-
-RSpec::Matchers.define :model_have_error_on_field do |expected|
-  match do |record|
-    record.valid? if record.errors.empty?
-
-    record.errors.key?(expected)
-  end
-
-  failure_message do |record|
-    keys = record.errors.attribute_names
-
-    "expect record.errors(#{keys}) to include #{expected}"
-  end
-end