Don't prepare script for script elements when src attribute is removed

[shannonbooth]

• At least two implementers are interested (and none opposed):
  • Already implemented (all browsers pass the WPT)
• Tests are written and can be reviewed and commented upon at:
  • https://github.com/web-platform-tests/wpt/blob/master/html/semantics/scripting-1/the-script-element/remove-src-attr-prepare-a-script.html
• Implementation bugs are filed:
  • Chromium: N/A
  • Gecko: N/A
  • WebKit: N/A
• Corresponding HTML AAM & ARIA in HTML issues & PRs: N/A
• MDN issue is filed: N/A
• The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

This is related to #12279 / #12282

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/scripting.html ( diff )

[annevk]

Thanks @shannonbooth!