[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/architecture.rst

@@ -29,8 +29,8 @@ up and maintained by the scripts from our :ref:`toolboxing`.
 
    Reference architecture of a public SearXNG setup.
 
-The reference installation activates ``server.limiter``, ``server.image_proxy``
-and ``ui.static_use_hash`` (:origin:`/etc/searxng/settings.yml
+The reference installation activates ``server.limiter`` and
+``server.image_proxy`` (:origin:`/etc/searxng/settings.yml
 <utils/templates/etc/searxng/settings.yml>`)
 
 .. literalinclude:: ../../utils/templates/etc/searxng/settings.yml