Revert "Add PROPERTIES argument to ecm_add_test and ecm_add_tests."

This reverts commit 0c224194.

Stephen Kelly pointed out that this is probably not the best approach to
the problem, and runs counter to the direction KDE's CMake code has been
going (splitting functions up and using CMake built-ins where possible).

I have a better solution in mind, which I'll post a review for later.

CCMAIL: kde-buildsystem@kde.org
CCBUG: 345797