cmd: event: Remove additional event description

The first name is taken from command name that's why shouldn't be listed in
help. The similar change was also done by commit a84d3b6c ("cmd: pwm:
Remove additional pwm description").
Also remove additional spaces in help message.

Before:
event event list   - list event spies

After:
event list   - list event spies

Signed-off-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Simon Glass <sjg@chromium.org>