Revert "edtlib: fix "last modified" semantic for included ... specs"

[1] was introduced to get more valuable answers from
the PropertySpec.path API, which is supposed to tell
in which file the property's specification was "last modfied".

Further work on related issues [2] showed that the
approach chosen in [1] is dead end: we need to first rethink
how bindings (and especially child-bindings) are initialized.

[1] edtlib: fix last modified semantic in included property specs
[2] edtlib: Preserve paths of properties from included child bindings

See also: #65221, #78095

This reverts commit b3b5ad81.

Signed-off-by: Christophe Dufaza <chris@openmarl.org>