merge_requests_controller_spec.rb

This shared example would take an object's database ID and create a
number of objects based on it. If for some reason the ID were a high
number, like 20, this would create `20 + 21 + 22` objects.

Not only was this dangerous from a performance perspective, it was
entirely unnecessary, as the behavior it was testing is already
well-tested in the unit test for the underlying object. For a controller
test, which is what's including this shared example, all we need to do
is verify that the assigned object contains the correct `id => object`
Hash, which is what we now test for.