Revert "Detect invalid uses of parent:: during compilation"

Revert "Detect invalid uses of parent:: during compilation"

This reverts commit a9e6667817c38f22f4645ec5b4e5c6b0e4b928fa.

Breakage found in the wild: Mockery uses a parent:: call in the
implementation regardless of whether the class has a parent or not:
https://github.com/mockery/mockery/blob/4324afeaf9d95b492507e6587abb3f024e2576de/library/Mockery/Mock.php#L600

This change is not worth the compat break in 7.4.