Remove failing test case

Oops, I missed this in e3a25dc.

spec/active_interaction/filters/model_filter_spec.rb

@@ -66,11 +66,9 @@ def self.name
       context 'inheritance shenanigans' do
         let(:case_equality) { false }
         let(:class_equality) { false }
-        let(:exact_equality) { false }
 
         before do
           allow(Model).to receive(:===).and_return(case_equality)
-          allow(value).to receive(:instance_of?).and_return(exact_equality)
           allow(value).to receive(:is_a?).and_return(class_equality)
         end
 
@@ -97,14 +95,6 @@ def self.name
             expect(result).to eql value
           end
         end
-
-        context 'with exact equality' do
-          let(:exact_equality) { true }
-
-          it 'returns the instance' do
-            expect(result).to eql value
-          end
-        end
       end
     end