runqemu: remove core-image-* whitelist

runqemu: remove core-image-* whitelist

Using a whitelist for image names to default to when none are
specified on the command line is no longer desired. Instead,
choose the most recently created image filename that conforms
to typical image naming conventions.

Fixes [YOCTO #5617].

(From OE-Core rev: 9f69e00200cdbd5ba2e46a54f33c29797816e43f)

Signed-off-by: Scott Garman <scott.a.garman@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>