The polyfill was added in [57492], but all browsers supported by WordPress already support import maps.
This not only disables the polyfill, but completely removes it as it was only added recently and there is no usage outside of core.
Props swissspidy, desrosj, luisherranz, gziolo.
Fixes#60970.
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git-svn-id: http://core.svn.wordpress.org/trunk@58348 1a063a9b-81f0-0310-95a4-ce76da25c4cd
