fix: correctly ignore optional deps when bundling vite deps

[haoqunjiang]

Description

Fixes #3977
Fixes #3850

😅 I've accidentally committed the actual fix in 25d86eb#diff-d17472499351c5bf75d44c67aaa203337dcce321fb578ff05302c61b2b2a3a8aR172

So this PR just removes the erroneous ingoreDepPlugin, and moves
the comments to the ignore option of the commonjs plugin.

The cause of the issues is this line: https://github.com/websockets/ws/blob/4c1849a61e773fe0ce016f6eb59bc3877f09aeee/lib/buffer-util.js#L105

When we ignore the optional deps when bundling, we expect
require('bufferutil') to throw an error.

However, with the previous ignoreDepPlugin implementation, the
require expression is turned into:

var bufferutil = {
	__proto__: null
};

var require$$1 = /*@__PURE__*/getAugmentedNamespace(bufferutil);

// ...

const bufferUtil = require$$1;

No error is thrown, so the code executes into the wrong branch.

After the fix, the require expression is left as-is. As bufferutil
is not installed in the user project, the error is thrown as expected.

Additional context

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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