ios: prepare for objc2 frameworks v0.3

These will have a bunch of default features enabled, so let's
pre-emptively disable them.

Author: madsmtm

Cargo.toml

@@ -38,7 +38,8 @@ ndk-context = "0.1"
 [target.'cfg(any(target_os = "ios", target_os = "tvos", target_os = "visionos"))'.dependencies]
 block2 = "0.5.0"
 objc2 = "0.5.1"
-objc2-foundation = { version = "0.2.0", features = [
+objc2-foundation = { version = "0.2.0", default-features = false, features = [
+    "std",
     "NSDictionary",
     "NSString",
     "NSURL",