mac frameworks: don't create bogus symlinks

the entry for the normal headers already ensures that there is the
correct version symlink. having an entry for the private headers as well
is pointless, and in fact clobbered the symlink for the actual library.

Change-Id: I2403761bf006b7bfa490ce85c7b0e46d5ef203c0
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>