version based on the git repository

This commit remove the need to update the brand for GIT_URL and GIT_BRANCH:
there are read from the git repository.

It is possible to call python -m searx.version freeze to freeze the current version.
Useful when the code is installed outside git (distro package, docker, etc...)

searx/settings_defaults.py

@@ -130,8 +130,6 @@ SCHEMA = {
         'contact_url': SettingsValue((None, False, str), None),
     },
     'brand': {
-        'git_url': SettingsValue(str),
-        'git_branch': SettingsValue(str),
         'issue_url': SettingsValue(str, None),
         'new_issue_url': SettingsValue(str, None),
         'docs_url': SettingsValue(str, None),