core/pkg-kconfig: run the kconfig fixups after exiting configurators

After we exit the configurators, we need to re-run the kconfig fixups to
ensure the user is not able to override them in the configurators.

Currently, we schedule that "for later", by removing the corresponding
stamp file, so make will run the fixups "later".

This means the user has access to the un-fixed .config file, which he
might decide to copy and use as a reference (not too bad, since we'd run
the fixups anyway; but not clean either).

Note that we still remove the stamp file before running the fixups, in
case any one of those fixups breaks, so we don't want to believe the
fixups have been applied; the fixup macro will touch that file anyway.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas De Schampheleire <patrickdepinguin@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>