internals: Remove double parenthesis in const_assert

The current `const_assert` macro is unused in the code base. We would
like to use it differently to how it was initially designed, remove the
parenthesis so it can be called directly in a module.

Author: tcharding

internals/src/macros.rs

@@ -139,9 +139,9 @@ macro_rules! debug_from_display {
 /// Asserts a boolean expression at compile time.
 #[macro_export]
 macro_rules! const_assert {
-    ($x:expr) => {{
+    ($x:expr) => {
         const _: [(); 0 - !$x as usize] = [];
-    }};
+    };
 }
 
 /// Derives `From<core::convert::Infallible>` for the given type.