Intent to unship: MathML scriptminsize and scriptsizemultiplier attributes

[Frédéric Wang]

This was suppposed to be sent one year ago, but I just realized about it
while cleaning some preferences recently.

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    Emilio removed remove scriptminsize and scriptsizemultiplier MathML
attributes on 2022-06-20. They have never been supported by any other
browsers.

    Bug to remove: https://bugzilla.mozilla.org/show_bug.cgi?id=1772697

Original intent to deprecate:
https://groups.google.com/g/mozilla.dev.platform/c/CSb-CaesGTo/m/1Z8pmYElBwAJ

Telemetry data for Firefox 102 showed very low usages:

https://georgf.github.io/usecounters/#kind=document&group=DEPRECATED&channel=beta&version=102

https://telemetry.mozilla.org/new-pipeline/dist.html#!cumulative=0&end_date=2022-07-05&include_spill=0&keys=__none__!__none__!__none__&max_channel_version=beta%252F102&measure=USE_COUNTER2_DEPRECATED_MathML_DeprecatedScriptminsizeAttribute_DOCUMENT&min_channel_version=nightly%252F71&processType=*&product=Firefox&sanitize=1&sort_by_value=0&sort_keys=submissions&start_date=2022-05-30&table=0&trim=1&use_submission_date=0https://telemetry.mozilla.org/new-pipeline/dist.html#!cumulative=0&end_date=2022-07-05&include_spill=0&keys=__none__!__none__!__none__&max_channel_version=beta%252F102&measure=USE_COUNTER2_DEPRECATED_MathML_DeprecatedScriptminsizeAttribute_PAGE&min_channel_version=nightly%252F71&processType=*&product=Firefox&sanitize=1&sort_by_value=0&sort_keys=submissions&start_date=2022-05-30&table=0&trim=1&use_submission_date=0


https://telemetry.mozilla.org/new-pipeline/dist.html#!cumulative=0&end_date=2022-07-05&include_spill=0&keys=__none__!__none__!__none__&max_channel_version=beta%252F102&measure=USE_COUNTER2_DEPRECATED_MathML_DeprecatedScriptsizemultiplierAttribute_DOCUMENT&min_channel_version=nightly%252F71&processType=*&product=Firefox&sanitize=1&sort_by_value=0&sort_keys=submissions&start_date=2022-05-30&table=0&trim=1&use_submission_date=0

https://telemetry.mozilla.org/new-pipeline/dist.html#!cumulative=0&end_date=2022-07-05&include_spill=0&keys=__none__!__none__!__none__&max_channel_version=beta%252F102&measure=USE_COUNTER2_DEPRECATED_MathML_DeprecatedScriptsizemultiplierAttribute_PAGE&min_channel_version=nightly%252F71&processType=*&product=Firefox&sanitize=1&sort_by_value=0&sort_keys=submissions&start_date=2022-05-30&table=0&trim=1&use_submission_date=0

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Frédéric Wang