Remove "command" string from logger

Since not all triggers are commands, removing the word `command` from
the logger so it is not confused with other types of triggers.

plugins/kernel_v2/config/vm_trigger.rb

@@ -117,7 +117,7 @@ module VagrantPlugins
         @command = command.to_sym
         @ruby_block = UNSET_VALUE
 
-        @logger.debug("Trigger defined for command: #{command}")
+        @logger.debug("Trigger defined for: #{command}")
       end
 
       # Config option `ruby` for a trigger which reads in a ruby block and sets