[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>

searx/settings_defaults.py

@@ -194,7 +194,6 @@ SCHEMA = {
     },
     'ui': {
         'static_path': SettingsDirectoryValue(str, os.path.join(searx_dir, 'static')),
-        'static_use_hash': SettingsValue(bool, False, 'SEARXNG_STATIC_USE_HASH'),
         'templates_path': SettingsDirectoryValue(str, os.path.join(searx_dir, 'templates')),
         'default_theme': SettingsValue(str, 'simple'),
         'default_locale': SettingsValue(str, ''),