Drop two fields nobody needed: session was a no-op, and no-unlock is the finger

Jorijn caught both.

`session` declared nothing. The FingerMatched signal is emitted for every
matched finger unconditionally -- it never consulted the config -- so a
`session` line was a rule the format invited you to write that did exactly
nothing. Announcing every finger is the right default anyway: a session agent
should not need a root-owned file to declare its interest in a signal it is
free to ignore. The column is gone.

Which leaves the config for the two things that really do need the daemon, and
with `session` gone the verdict column had no partner left to vary against. It
read as a property of the finger while being a property of the attempt, so it
is now written as what it is:

    <finger>  [no-unlock]  [absolute command...]

no-unlock says the finger never unlocks; a command is what root runs. At least
one is required, because a finger listed alone says nothing the signal does not
already say -- and that is a parse error rather than a silently useless line.

The example config now also states plainly what no-unlock is not. It is a panic
button, not deniability: the rejection it fabricates comes back in milliseconds
where a real one takes about three seconds, the journal records that the finger
actually matched, the file names the finger in plain text, and the finger still
shows as enrolled. Both of those weaknesses are real and neither is fixed here.

packaging/APKBUILD

@@ -10,7 +10,7 @@
 # Alpine, so an APKBUILD that compiled from source could not be built by
 # anyone but us either.
 pkgname=fingerprintd
-pkgver=0.2.0
+pkgver=0.2.1
 pkgrel=0
 pkgdesc="Fingerprint daemon for the Fairphone 6 (FocalTech FT9391 behind QTEE)"
 url="https://forgejo.catcrafts.net/Catcrafts/fingerprintd"