Remove no_proxy variables

no_proxy was newer supported by debmirror
also allow empty *_proxy env values in order to bypass
system-defined proxy settings

Closes-bug: PROD-35868
Change-Id: Id55cd877f6af3a9dd52e0c16a720fa9efe620c0c
diff --git a/README.rst b/README.rst
index c10a6ad..715cc89 100644
--- a/README.rst
+++ b/README.rst
@@ -22,7 +22,6 @@
               https_proxy: "url"
               ftp_proxy: "url"
               rsync_proxy: "url"
-              no_proxy: ['val1', 'val2']
               force: False
               lock_target: True
               extra_flags: [ '--verbose', '--progress', '--nosource', '--no-check-gpg', '--rsync-extra=none' ]
@@ -58,6 +57,10 @@
 directories which are using current cache. By removing this file you will flush
 cache and lead to update all repos during next state run.
 
+Set of `X_proxy` parameters could be set to empty line to overwrite proxy
+settings defined in environment variables. This serves like NO_PROXY setting
+which is not supported by debmirror.
+
 **Documentation and bugs**
 
 * http://salt-formulas.readthedocs.io/