[fix] documentation - remove brand.git_url & brand.git_branch

In commit 4b43775c the brand.git_url & brand.git_branch has been removed, with
this patch these settings are removed from the documentation.

docs/admin/engines/settings.rst
  - Remove brand.git_url & brand.git_branch

docs/dev/makefile.rst
  - Remove brand.git_url & brand.git_branch

modified   docs/dev/lxcdev.rst
  - Remove brand.git_url & brand.git_branch
  - fix searXNG to SearXNG

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