chore(pacman): require signed DB for antergos-pkgs, drop TrustAll

Both build and installed-system pacman configs now use
'SigLevel = DatabaseRequired PackageOptional' for [antergos-pkgs].
The repo DB is signed by the dedicated signing key (AA644A09...),
which authenticates all packages via the checksums the signed DB
carries. Keyring package updated to match.

iso-profiles/antergos/root-overlay/etc/pacman.conf

@@ -22,7 +22,7 @@ LocalFileSigLevel = Optional
 
 # Antergos NeXT custom packages repo
 [antergos-pkgs]
-SigLevel = Optional TrustAll
+SigLevel = DatabaseRequired PackageOptional
 Server = https://antergos-next.github.io/antergos-packages/
 
 [system]

pacman.conf.d/iso-x86_64.conf

@@ -76,7 +76,7 @@ LocalFileSigLevel = Optional
 # Include = /etc/pacman.d/mirrorlist
 
 [antergos-pkgs]
-SigLevel = Optional TrustAll
+SigLevel = DatabaseRequired PackageOptional
 Server = https://antergos-next.github.io/antergos-packages/
 
 [system]