Fix type generation for types named AttachedClass that are not T::Types::AttachedClassType

[Morriar]

Motivation

When defining a class named AttachedClass, Tapioca is incorrectly generating it as if it was the type T.attached_class.

So for the following Ruby code:

class Foo
  class AttachedClass; end

  sig { returns(AttachedClass) }
  def foo; end
end

Tapioca would generate the following RBI which is incorrect:

class Foo
  class AttachedClass; end

  sig { returns(::Foo::T.attached_class) }
  def foo; end
end

Implementation

The gsub on the type name was a workaround until we merged sorbet/sorbet#3380 in sorbet-runtime, this is now unnecessary and is actually broken. We can just remove it.

Tests

See automated tests.