bitbake wasn't reparsing when _remove items were added to its configuration
and equally, appends/prepends were also being badly tracked. This
change enrures these variables are accounted for in the configuration
hash.
[YOCTO #5172]
(Bitbake rev: 62914f9208ef2427a34daa523af857f4027900eb)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>