flatpak: Switch to using Adelie Linux a52dec

Original repo is removed, change to maintained fork.
Others are doing the same e.g. FreeBSD

pkgs/flatpak/testing/liba52.json

@@ -0,0 +1,24 @@
+{
+    "name": "liba52",
+    "config-opts": [ "--enable-shared", "--disable-static" ],
+    "rm-configure": true,
+    "cleanup": [ "/bin/*a52*" ],
+    "sources": [
+        {
+            "type": "archive",
+            "url": "https://distfiles.adelielinux.org/source/a52dec/a52dec-0.8.0.tar.gz",
+            "sha256": "03c181ce9c3fe0d2f5130de18dab9bd8bc63c354071515aa56983c74a9cffcc9"
+        },
+        {
+            "type": "patch",
+            "path": "a52dec-configure-optflags.patch"
+        },
+        {
+            "type": "script",
+            "commands": [
+                "autoreconf -fiv"
+            ],
+            "dest-filename": "autogen.sh"
+        }
+    ]
+}