Remove resolveId hook and load hook from asset-plugin

[queq1890]

While walking through proxx's Rollup config, I found that id with asset-url: prefix no longer exists.
So I think we can remove resolveId hook and load hook that used to deal with such ids.

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[queq1890]

@googlebot I signed it!

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[jakearchibald]

That's fair, although it's a pattern we use on other projects, and the code isn't doing any harm (it doesn't end up in a client bundle). I guess we should publish the asset plugin to npm.

[queq1890]

@jakearchibald

it's a pattern we use on other projects, and the code isn't doing any harm (it doesn't end up in a client bundle)

makes sense to me. Thank you for the quick response 😄