!fixup ffi cargo.toml

Author: Hywan

bindings/matrix-sdk-ffi/Cargo.toml

@@ -73,6 +73,7 @@ features = [
     "e2e-encryption",
     "experimental-oidc",
     "experimental-sliding-sync",
+    "experimental-not-simplified-sliding-sync", # we don't want simplified MSC3575 yet!
     "experimental-widgets",
     "markdown",
     "native-tls", # note: differ from block above