message: Move an if/panic into an assert
  Summary: Better to be consistent, and clippy suggested it to me.
diff: @@ -267,12 +267,12 @@ impl GlobalsStatic {
  /// value. If populated via a `#[starlark_module]`, that means a single function in it.
  pub fn function(&'static self, x: impl FnOnce(&mut GlobalsBuilder)) -> FrozenValue {
  let globals = self.globals(x);
  - if globals.0.variables.len() != 1 {
  - panic!(
  + assert!(
  + globals.0.variables.len() == 1,
  "GlobalsBuilder.function must have exactly 1 member, you had {:?}",
  globals.names()
  );
  - }
  +
  *globals.0.variables.values().next().unwrap()
  }
  