Remove unused "platform-version" property from core/applications POMs

This commit removes the (apparently unused) `platform-version` property from the `core` and `applications` POMs.

Also, aren't they wrong?
* For the Kepler (4.3) profile, it's set to `[4.2,4.3)` (i.e. include 4.2, exclude 4.3).
* For the Luna (4.4) profiles, it's set to `[4.3,4.4)` (i.e. include 4.3, exclude 4.4).