The getExtraFields callback added in 6456149 dumped entire page content
as a single extraFields string. plugin-search joins title+extraFields
with .join(' ') and runs a RegExp against the result for every page on
every keystroke — multi-kilobyte strings per page caused 2–3 s blocking
tasks, freezing the page.
Fix: remove getExtraFields (and the now-unused normalizeSearchText /
htmlEntityMap helpers), restoring the pre-regression search coverage
(page titles + section headings).
