Remove phobos dependency from issue 4003 test case
fix Issue 10938 - ICE on recursive instantiation in opDispatch

By fixing issue 10736 (314a1cca9ff56775b9e2a9cf81564135be0726b1), all of template instance semantic are reliably finished by the deferred mechanism.
And it had removed the necessity of the code in `DotTemplateInstanceExp::semanticY` for the issue 4003.

Therefore, just remove the unnecessary code to fix the ICE.