profiles/Makefile: Clean up rules to better support extra profiles

In the course of preparing !1207, I found that the validation rules in profiles/Makefile did not take kindly to the new profiles/apparmor/profiles/extras/abstractions/ directory. I tried a couple rounds of quick fixes, but it became clear that the rules as currently written were just not amenable to the new addition, and needed more attention than I could give it by-the-by.

So I separated out that commit, and revised the makefile more thoroughly. The updated rules now rely more on find(1) than $(wildcard), and have a number of [what I believe to be] small quality-of-life improvements. Taken together, make check passes cleanly with the new files from my other MR present.

One thing I noticed was that the profiles under apparmor.d/ were not previously being checked for the include if exists <local/*> bit---only the ones under extras/. I've thus included a fix to the sbuild-shell profile, which fortunately was the only one that failed the check.

Note that at present, you'll get a couple of harmless find: ‘./apparmor/profiles/extras/abstractions’: No such file or directory errors when running the checks, since that directory won't appear until the other MR is merged. I figure, better to bear that for now, and not have to touch the makefile again later.

NOTE: The CI pipeline here will need to be updated to invoke the check-local target instead of check-extras. This target was renamed as it is no longer limited in scope to the profiles under extras/.