Move excluded_terms filter in `get_adjacent_post()`.

The filter was added in 4.4 [34528] #9571, but in a place where it could not
affect the adjacent post query.

Fixes #35211.
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git-svn-id: https://core.svn.wordpress.org/trunk@36043 1a063a9b-81f0-0310-95a4-ce76da25c4cd