Revert "FIX: Return error if new topic category not found"

This reverts commit 9c606dd99a7ce227bde38527986b250d6e6c22dc.

spec/requests/posts_controller_spec.rb

@@ -775,20 +775,6 @@ describe PostsController do
         }
         expect(response.status).to eq(403)
       end
-
-      it 'will raise an error if specified category cannot be found' do
-        user = Fabricate(:admin)
-        master_key = ApiKey.create_master_key.key
-
-        post "/posts.json", params: {
-          api_username: user.username,
-          api_key: master_key,
-          title: 'this is a test title',
-          raw: 'this is test body',
-          category: 'invalid'
-        }
-        expect(response.status).to eq(404)
-      end
     end
 
     describe "when logged in" do