[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/installation-searxng.rst

@@ -86,7 +86,6 @@ below. This setup:
 
 - enables :ref:`limiter <limiter>` to protect against bots
 - enables :ref:`image proxy <image_proxy>` for better privacy
-- enables :ref:`cache busting <static_use_hash>` to save bandwidth
 
 Modify the ``/etc/searxng/settings.yml`` to your needs:
 
@@ -129,4 +128,3 @@ configuration file.
 If everything works fine, hit ``[CTRL-C]`` to stop the *webapp* and disable the
 debug option in ``settings.yml``. You can now exit SearXNG user bash session (enter exit
 command twice).  At this point SearXNG is not demonized; uwsgi allows this.
-