[mod] reduce enviroment variables in shell scripts to what is needed

Not all settings from the 'brand:' section of the YAML files are needed in the
shell scripts.  This patch reduce the variables in ./utils/brand.env to what is
needed.  The following ('brand:' settings) can be removed from this file:

- ISSUE_URL
- DOCS_URL
- PUBLIC_INSTANCES
- WIKI_URL

Tasks running outside of an *installed instance*, need the following settings
from the YAML configuration:

- GIT_URL            <--> brand.git_url
- GIT_BRANCH         <--> brand.git_branch
- SEARX_URL          <--> server.base_url  (aka PUBLIC_URL)
- SEARX_PORT         <--> server.port
- SEARX_BIND_ADDRESS <--> server.bind_address

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/settings.yml

@@ -4,15 +4,16 @@ general:
   contact_url: false        # mailto:contact@example.com
 
 brand:
-  # If you change a value in this section don't forget to rebuild instance's
-  # enviroment (make buildenv)
-  git_url: https://github.com/searxng/searxng
-  git_branch: master
-  issue_url: https://github.com/searxng/searxng/issues
   new_issue_url: https://github.com/searxng/searxng/issues/new
   docs_url: https://searxng.github.io/searxng
   public_instances: https://searx.space
   wiki_url: https://github.com/searxng/searxng/wiki
+  issue_url: https://github.com/searxng/searxng/issues
+
+  # If you change a value below don't forget to rebuild instance's enviroment
+  # (make buildenv)
+  git_url: https://github.com/searxng/searxng
+  git_branch: master
 
 search:
   # Filter results. 0: None, 1: Moderate, 2: Strict
@@ -32,13 +33,14 @@ search:
   formats: [html, csv, json, rss]
 
 server:
+  # If you change port, bind_address or base_url don't forget to rebuild
+  # instance's enviroment (make buildenv)
   port: 8888
   bind_address: "127.0.0.1"
+  base_url: false  # Possible values: false or "https://example.org/location".
 
-  # Set custom base_url. Possible values: false or "https://example.org/location"
-  # If you change base_url don't forget to rebuild instance's enviroment (make
-  # buildenv) port & address to listen on
-  base_url: false
+  # If your instance owns a /etc/searx/settings.yml file, then set the following
+  # values there.
 
   secret_key: "ultrasecretkey"  # change this!
   # Proxying image results through searx