Say "memory" instead of "__wasi_memory" in error messages.

While the "__wasi_memory" name is something we considered, the name
currently being used for the memory exported to WASI is "memory", so
adjust the error message accordingly.

wasmtime-wasi/src/syscalls.rs

@@ -30,7 +30,7 @@ fn get_memory(vmctx: &mut VMContext) -> Result<&mut [u8], host::__wasi_errno_t>
             )),
             x => {
                 println!(
-                    "!!! no export named __wasi_memory, or the export isn't a mem: {:?}",
+                    "!!! no export named \"memory\", or the export isn't a mem: {:?}",
                     x
                 );
                 Err(host::__WASI_EINVAL)