bitbake/data_smart: Change overrides behaviour to remove expanded variables from...

bitbake/data_smart: Change overrides behaviour to remove expanded variables from the datastore

Currently if you do:

OVERRIDES = "z"
DEPENDS_prepend = "a "
DEPENDS = "b"
DEPENDS_z = "c"

d.update_data()
d.getVar("DEPENDS")

gives "a c"

d.update_data()
d.getVar("DEPENDS")

then gives "c"

This patch changes the behaviour such that at the time bitbake expands the DEPENDS_z
override, it removes "DEPENDS_z" from the data store. In the above example this would
mean that it wouldn't matter how often you call d.update_data(), you'd always get
"a c" back.

See the bitbake-devel mailing list for further discussion and analysis of the
potential impact of this change.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>