[Markdown] Remove summary and seoSummary from the JS docs

[wbamberg]

As described in #3923, this issue is to remove the summary and seoSummary classes from the JS docs.

There are four categories:

1. the summary or seoSummary classes are not present
2. the summary or seoSummary classes just select the first paragraph anyway
3. the summary or seoSummary classes truncates the first paragraph
4. the summary or seoSummary classes select a completely different text.

Out of 922 total pages, the breakdown across these four categories is:

1. summary not present                  817
2. summary selects first paragraph       81
3. summary truncates first paragraph     22
4. summary selects different text         2

This issue is to fix categories 3 and 4. Category 2 can be fixed in the conversion if we ask the convertor to just discard these classes.

The list of pages in category 3:

https://github.com/mdn/content/blob/main/files/en-us/web/javascript/eventloop/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/guide/numbers_and_dates/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/classes/static/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/date/date/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/date/getday/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/date/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/map/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/math/abs/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/math/cos/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/number/isfinite/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/rangeerror/rangeerror/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/reflect/preventextensions/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/reflect/setprototypeof/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/string/padstart/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/string/raw/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/string/replace/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/global_objects/string/replaceall/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/operators/conditional_operator/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/statements/async_function/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/statements/import/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/typed_arrays/index.html

The list of pages in category 4:

https://github.com/mdn/content/blob/main/files/en-us/web/javascript/guide/iterators_and_generators/index.html
https://github.com/mdn/content/blob/main/files/en-us/web/javascript/reference/operators/optional_chaining/index.html