build/linux: Drop 'cfitsio' for now due to security concerns

Temporarily drops 'cfitsio' which started weeks ago to change its hash.
In my tests, after "fixing" the hash, sometimes it alternates to another,
which breaks the build again. This is too hard to maintain and unsafe(?).

build/linux/flatpak/org.gimp.GIMP-nightly.json.in

@@ -712,26 +712,6 @@
                 }
             ]
         },
-        {
-            "name": "cfitsio",
-            "config-opts": [
-                "--enable-reentrant"
-            ],
-            "make-args": ["shared"],
-            "cleanup": [
-                "/include",
-                "/lib/*.a",
-                "/lib/*.la",
-                "/lib/pkgconfig"
-            ],
-            "sources": [
-                {
-                    "type": "archive",
-                    "url": "http://heasarc.gsfc.nasa.gov/FTP/software/fitsio/c/cfitsio-4.2.0.tar.gz",
-                    "sha256": "eba53d1b3f6e345632bb09a7b752ec7ced3d63ec5153a848380f3880c5d61889"
-                }
-            ]
-        },
         {
             "name": "babl",
             "buildsystem": "meson",