staging: Ensure dependencies are removed before being added
Currently items are added to the sysroot, the obsolete items are removed. If
a change such as pkgconfig -> pkgconf is made, this leads to conflicts of
overlapping files in the sysroot.
In order to better support this, handle removing items before adding them.
This requires some minor refactoring to construct the installed list
before the main function loop, otherwise there are no changes in this
patch other than reordering the operations.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
