postgresql: simplify systemdSupport default value

systemd is not available on static platforms, so the isStatic check is
redundant.

pkgs/servers/sql/postgresql/generic.nix

@@ -9,8 +9,7 @@ let
 
       , removeReferencesTo, writeShellApplication
 
-      # This is important to obtain a version of `libpq` that does not depend on systemd.
-      , systemdSupport ? lib.meta.availableOn stdenv.hostPlatform systemdLibs && !stdenv.hostPlatform.isStatic
+      , systemdSupport ? lib.meta.availableOn stdenv.hostPlatform systemdLibs
       , enableSystemd ? null
       , gssSupport ? with stdenv.hostPlatform; !isWindows && !isStatic