keep compile check only in runtime

Author: Shubham8287

crates/engine/src/lib.rs

@@ -1,11 +1,3 @@
-#[cfg(all(feature = "tokio", feature = "simulation"))]
-compile_error!(
-    "spacetimedb-engine requires exactly one runtime backend: enable either `tokio` or `simulation`, not both"
-);
-
-#[cfg(not(any(feature = "tokio", feature = "simulation")))]
-compile_error!("spacetimedb-engine requires exactly one runtime backend: enable either `tokio` or `simulation`");
-
 pub mod db;
 pub mod error;
 pub mod metrics;

crates/runtime/src/lib.rs

@@ -1,8 +1,8 @@
-//#[cfg(all(feature = "tokio", feature = "simulation"))]
-//compile_error!(
-//    "spacetimedb-runtime requires exactly one runtime backend: enable either `tokio` or `simulation`, not both"
-//);
-//
+#[cfg(all(feature = "tokio", feature = "simulation"))]
+compile_error!(
+   "spacetimedb-runtime requires exactly one runtime backend: enable either `tokio` or `simulation`, not both"
+);
+
 #[cfg(not(any(feature = "tokio", feature = "simulation")))]
 compile_error!("spacetimedb-runtime requires exactly one runtime backend: enable either `tokio` or `simulation`");