Remove at-block source code from search index #1929
Description
It looks like that for the at-blocks, we just write the contents of the original code block to the search index.
A case in point: we can "find" a bunch of spurious DocTestSetups in the Julia manual (https://docs.julialang.org/en/v1.8.1/search/?q=doctestsetup) which do not appear in the HTML, due to at-meta blocks on those pages.