Remove HashFilter.transform_keys

lib/active_interaction/backports.rb

@@ -64,15 +64,4 @@ def delete_with_details(attribute)
     end
     include Details unless method_defined?(:details)
   end
-
-  class HashFilter # rubocop:disable Style/Documentation
-    # Required for Rails < 4.0.0.
-    def self.transform_keys(hash, &block)
-      return hash.transform_keys(&block) if hash.respond_to?(:transform_keys)
-
-      result = {}
-      hash.each_key { |key| result[block.call(key)] = hash[key] }
-      result
-    end
-  end
 end

spec/active_interaction/filters/hash_filter_spec.rb

@@ -6,16 +6,6 @@
   include_context 'filters'
   it_behaves_like 'a filter'
 
-  context 'backports' do
-    describe '.transform_keys' do
-      it 'transforms keys' do
-        original = { 'key' => 'value' }
-        transformed = described_class.transform_keys(original, &:to_sym)
-        expect(transformed).to eql(key: 'value')
-      end
-    end
-  end
-
   context 'with a nested nameless filter' do
     let(:block) { proc { hash } }