Remove `feature(alloc)` declarations which are no longer needed.

wasmtime-environ/src/lib.rs

@@ -25,7 +25,6 @@
     )
 )]
 #![no_std]
-#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 #[cfg(not(feature = "std"))]
 #[macro_use]

wasmtime-jit/src/lib.rs

@@ -22,7 +22,6 @@
     )
 )]
 #![no_std]
-#![cfg_attr(not(feature = "std"), feature(alloc))]
 
 #[cfg(not(feature = "std"))]
 #[macro_use]