Support simple search for legacy repository

[abn]

Add support for simple search in legacy repositories.

Resolves: https://github.com/python-poetry/poetry/issues/2446

Remove unwanted stubbing of LegacyRepository.packages.

This change removes a stubbing change added in 46ae4f5. This change was incorrect, as the base class already sets package list to an empty list.

The test case was also incorrect as it forced addition to internal package list.