Fix runtime not properly unloading on webpack

[quexten]

On Webpack, the cache expects exports on a required module to stay the same. The dist/argon2.js module deletes the export when calling unload runtime. On Webpack builds, if you unload the runtime, and then load it again by doing a hash, the require never resolves.

This PR fixes this behavior by deleting the module form the cache entirely, when unloading the runtime.