build-aux: Update libdatachannel for Flatpak

This updates libdatachannel to the commit supporting simulcast [1]
and removes the now unnecessary libdatachannel patching.

[1] https://github.com/paullouisageneau/libdatachannel/commit/709a66339451bb4c8d4e5ced78c67605ec09da31

Signed-off-by: pkv <[email protected]>

build-aux/modules/50-libdatachannel.json

@@ -13,8 +13,8 @@
             "type": "git",
             "url": "https://github.com/paullouisageneau/libdatachannel.git",
             "disable-submodules": true,
-            "tag": "v0.19.0-alpha.1",
-            "commit": "f66f2813c11acaea3b20d9a5f115823777426e63"
+            "tag": "v0.19.0-alpha.4",
+            "commit": "709a66339451bb4c8d4e5ced78c67605ec09da31"
         }
     ]
 }