Removes the keys() function from the MulticonfigCache. This appears to
be a leftover from before the class inherited from collections.Mapping,
is now unnecessary, and was outright incorrect.
(Bitbake rev: 5f37b6d2829fcac1f16602d9697f8bfbcb65ff62)
Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>