A previous change meant image/sdk recipes were removed unconditionally
by the class and did not respect RM_WORK_EXCLUDE. This fixes that
problem.
[YOCTO #7114]
(From OE-Core rev: 050de16968fe6efeba5d64761b11512549e9fdc2)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>