xastir: switch from imagemagick6 to graphicsmagick

This removes the need for the CVE addled imagemagick6. This approach
is similar to what is done on the BSDs:

https://github.com/openbsd/ports/blob/master/comms/xastir/Makefile

pkgs/applications/misc/xastir/default.nix

···
 { lib, stdenv, fetchFromGitHub, autoreconfHook, pkg-config
 , curl, db, libgeotiff
 , xorg, motif, pcre
-, perl, proj, rastermagick, shapelib
+, perl, proj, graphicsmagick, shapelib
 , libax25
 }:
 
···
   buildInputs = [
     curl db libgeotiff
     xorg.libXpm xorg.libXt motif pcre
-    perl proj rastermagick shapelib
+    perl proj graphicsmagick shapelib
     libax25
   ];
 

pkgs/top-level/all-packages.nix

···
 
   xaos = libsForQt5.callPackage ../applications/graphics/xaos { };
 
-  xastir = callPackage ../applications/misc/xastir {
-    rastermagick = imagemagick6;
-  };
+  xastir = callPackage ../applications/misc/xastir { };
 
   xautomation = callPackage ../tools/X11/xautomation { };