refactor(v2): remove type attribute from link and script tags

[lex111]

Motivation

These are completely unnecessary attributes that are actually already being removed by the minifier (terser), so we can remove them from the codebase itself.

The default type for resources given by the stylesheet keyword is "text/css" (see w3.org/TR/html5/links.html#link-type-stylesheet)
For scripts, default type is "text/javascript" (see http://www.w3.org/TR/html5/scripting-1.html#attr-script-type)

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Preview

Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/docusaurus, and link to your PR here.)

[slorber]

👍

[netlify]

✔️ [V1]

🔨 Explore the source changes: a0e0d9b

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-1/deploys/60c0a89e5a932f000742345b

😎 Browse the preview: https://deploy-preview-4907--docusaurus-1.netlify.app

[netlify]

✔️ [V2]

🔨 Explore the source changes: a0e0d9b

🔍 Inspect the deploy log: https://app.netlify.com/sites/docusaurus-2/deploys/60c0a89e21a9a50007d944d0

😎 Browse the preview: https://deploy-preview-4907--docusaurus-2.netlify.app

[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	64
🟢 Accessibility	97
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-4907--docusaurus-2.netlify.app/

[github-actions]

Size Change: -897 B (0%)

Total Size: 620 kB

Filename	Size	Change
website/build/assets/css/styles.********.css	87.7 kB	-622 B (-1%)
website/build/blog/2017/12/14/introducing-docusaurus/index.html	62.1 kB	-160 B (0%)
website/build/index.html	27 kB	-99 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
website/build/assets/js/main.********.js	443 kB	-16 B (0%)
website/build/docs/introduction/index.html	235 B	0 B

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