rust: remove uses of #[no_mangle]

Mangled symbols do not cause any issue; disabling mangling is only useful if
C headers reference the Rust function, which is not the case here.

Reviewed-by: Junjie Mao <junjie.mao@hotmail.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/qemu-api/src/definitions.rs

@@ -53,7 +53,6 @@ macro_rules! module_init {
         #[cfg_attr(target_os = "windows", link_section = ".CRT$XCU")]
         pub static LOAD_MODULE: extern "C" fn() = {
             extern "C" fn __load() {
-                #[no_mangle]
                 unsafe extern "C" fn $func() {
                     $body
                 }