Fixes path issue in derive-impl (#1823)

Needs https://github.com/sam0x17/macro_magic/pull/13

The associated PR allows the export of tokens from macro_magic at the
specified path. This fixes the path issue in derive-impl. Now, we can
import the default config using the standard rust syntax:

```rust
use frame_system::config_preludes::TestDefaultConfig;

[derive_impl(TestDefaultConfig as frame_system::DefaultConfig)]
impl frame_system::DefaultConfig for Test {
   //....
}
```