[OE-core] weird exports in bitbake.conf

[Phil Blundell]

Does anybody know why these vars are exported (or, in the case of
STAGING_IDLDIR, there at all)?

export QMAKE_MKSPEC_PATH = "${STAGING_DATADIR_NATIVE}/qmake"
export STAGING_SIPDIR = "${STAGING_DATADIR_NATIVE}/sip"
export STAGING_IDLDIR = "${STAGING_DATADIR}/idl"

p.