Revert shared taxonomy term splitting for 4.1.

This is a revert of [30494], [30492], [30347], and [30334]. The latter
changeset was a revert of [30336], which was a revert of [30241].

Watch for Term Splitting, Version III in version 4.2, coming soon to a
WordPress trunk near you.

See #30335, #5809.
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Editor: limit scrolling triggered when TinyMCE is auto-resized to 100px. Prevents auto-scrolling on page load. Fixes #30515.
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