build(vcpkg): use a minimal libqrencode build

`libpng` in vcpkg doesn't have the right patches (libpng@ed68998) to
build with universal binary support on macOS, so let's avoid building it
(we need to bump our baseline for this too)

Thanks for letting me know it was optional, Kode :)

Signed-off-by: Seth Flynn <getchoo@tuta.io>

vcpkg.json

@@ -2,9 +2,18 @@
   "dependencies": [
     "bzip2",
     "cmark",
-    { "name": "ecm", "host": true },
-    "libqrencode",
-    { "name": "pkgconf", "host": true },
+    {
+      "name": "ecm",
+      "host": true
+    },
+    {
+      "name": "libqrencode",
+      "default-features": false
+    },
+    {
+      "name": "pkgconf",
+      "host": true
+    },
     "tomlplusplus",
     "zlib"
   ]