[enh] py: drop deps (#5407)

The difference between decompression with brotli or gzip in HTML files is
negligible for 3 MB of compiled binary package.

Introduced in https://github.com/searxng/searxng/commit/eaa694fb7d0e47b943bc6d6edb6cb6a40ab2d85e

Closes https://github.com/searxng/searxng/security/code-scanning/276
Closes https://github.com/searxng/searxng/security/dependabot/37

searx/webapp.py

@@ -1040,7 +1040,6 @@ def image_proxy():
         request_headers = {
             'User-Agent': gen_useragent(),
             'Accept': 'image/webp,*/*',
-            'Accept-Encoding': 'gzip, deflate',
             'Sec-GPC': '1',
             'DNT': '1',
         }