Remove code that was needed to support old searx instances

[return42]

After old searx instances has been removed from the list

• Dropping the support for SearX instances on searx.space and in this repository. searx-instances#336
• Add notice that SearX instances will get removed #141
• [mod] Add notice that SearX instances will get removed #144

we can do some code cleanups.

Debian

• https://github.com/searxng/searx-space/blob/master/searxstats/data/fetch_deb_hashes.py

searx-space/searxstats/config.py

Lines 62 to 65 in f254f04

	# debian
	DEBIAN_GIT_URL = 'https://salsa.debian.org/debian/searx'
	DEBIAN_SOURCE_PACKAGE_NAMES = [
	'searx', 'twitter-bootstrap3', 'jquery', 'leaflet', 'requirejs', 'typeahead.js']

What else?

This is a non-exhaustive list / hints are welcome

[dalf]

• https://github.com/search?q=repo%3Asearxng%2Fsearx-space%20SEARX_GIT_REPOSITORY%20&type=code

• searx-space/searxstats/config.py

  Line 69 in 3603b08

  'https://github.com/searx/searx',

• searx-space/searxstats/config.py

  Lines 71 to 72 in 3603b08

  	'https://salsa.debian.org/debian/searx',
  	'https://gitlab.e.foundation/e/cloud/my-spot',

• Since all SearXNG instances support the simple theme: this part and usage of this part can be removed
  

  searx-space/searxstats/fetcher/timing.py

  Lines 71 to 76 in 3603b08

  	'oscar': CheckResult(
  	results=etree.XPath("//div[@id='main_results']/div[contains(@class,'result-default')]"),
  	engines=etree.XPath("//span[contains(@class, 'label label-default')]"),
  	alert_danger_main=etree.XPath("//div[contains(@class, 'alert-danger')]/p[2]"),
  	alter_danger_side=etree.XPath("//div[contains(@class, 'alert-danger')]/text()"),
  	),