[mod] remove option ui.static_use_hash (cache busting) (#5004)

Cache busting has caused serious problems for users in the past, here are two
examples:

- https://github.com/searxng/searxng/issues/4419
- https://github.com/searxng/searxng/issues/4481

And it makes development and deployment significantly more complex because it
binds the client side to the server side:

- https://github.com/searxng/searxng/pull/4466

In the light of a decoupled development of the WEB clients from the server side:

- https://github.com/searxng/searxng/pull/4988

is it appropriate to abandon this feature. In fact,  it has been ineffective
since #4436 anyway.

However, the benefit has always been questionable, since at best only a few kB
of data are saved (at least in the context of an image_proxy, the effect is below
the detection limit). Ultimately, the client is responsible for caching.

Related: https://github.com/searxng/searxng/issues?q=label%3A%22clear%20browser%20cache%22

Closes: https://github.com/searxng/searxng/pull/4466
Closes: https://github.com/searxng/searxng/issues/1326
Closes: https://github.com/searxng/searxng/issues/964

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/admin/update-searxng.rst

@@ -58,10 +58,6 @@ and then, to name just a few:
 - Bot protection has been switched from filtron to SearXNG's :ref:`limiter
   <limiter>`, this requires a :ref:`Valkey <settings valkey>` database.
 
-- To save bandwidth :ref:`cache busting <static_use_hash>` has been implemented.
-  To get in use, the ``static-expires`` needs to be set in the :ref:`uwsgi
-  setup`.
-
 To stay tuned and get in use of the new features, instance maintainers have to
 update the SearXNG code regularly (see :ref:`update searxng`).  As the above
 examples show, this is not always enough, sometimes services have to be set up