Revert "Fix conditional attributes in exported allocator name. (proxy-wasm#299)"

This reverts commit c502d38.

Author: Javier Atadia

src/allocator.rs

@@ -18,7 +18,7 @@ use std::mem::MaybeUninit;
     all(target_arch = "wasm32", target_os = "unknown"),
     export_name = "malloc"
 )]
-#[cfg_attr(not(all(target_arch = "wasm32", target_os = "unknown")), no_mangle)]
+#[no_mangle]
 pub extern "C" fn proxy_on_memory_allocate(size: usize) -> *mut u8 {
     let mut vec: Vec<MaybeUninit<u8>> = Vec::with_capacity(size);
     unsafe {