core/pkg-generic: only save latest package list

core/pkg-generic: only save latest package list

When rebuilding a package, simply appending the package's file list to
the global list means that the package list grows for every rebuild, as
does the time taken to check for files installed by multiple packages.
Furthermore, we get false positives where a file is reported as being
installed by multiple copies of the same package.

With this approach we may end up with orphaned files in the target
filesystem if a package that has been updated and rebuilt no longer
installs the same set of files, but we know that only a clean build will
produce reliable results.  In fact it may be helpful to identify these
orphaned files as evidence that the build is not clean.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>