doc: remove local version of Sphinx searchtools.js

We previously created an improved version of searchtools.js (used by the
Sphinx search) to remove the reST tags shown in the search results.
This has now been fixed in the upstream version of searchtools.js along
with other speed and visual improvements, so we should remove our local
copy.

Signed-off-by: David B. Kinder <[email protected]>

Author: dbkinder