Remove 'non-interactive-mode' option for Agent 'enroll' command (#652)

This is a forward fit of
elastic/ingest-docs#1668 into the 9.0 docs.

Author: kilfoyle

reference/ingestion-tools/fleet/agent-command-reference.md

@@ -182,7 +182,6 @@ elastic-agent enroll --fleet-server-es <string>
                      [--force]
                      [--header <strings>]
                      [--help]
-                     [--non-interactive]
                      [--proxy-disabled]
                      [--proxy-header <strings>]
                      [--proxy-url <string>]
@@ -307,9 +306,6 @@ For more information about custom certificates, refer to [Configure SSL/TLS for
     We strongly recommend that you use a secure connection.
 
 
-`--non-interactive`
-:   Install {{agent}} in a non-interactive mode. This flag is helpful when using automation software or scripted deployments. If {{agent}} is already installed on the host, the installation will terminate.
-
 `--proxy-disabled`
 :   Disable proxy support including environment variables.