scripts: Use tpe instead of type_, again

The .rst generation doesn't escape the trailing `_` and the docs build
gets upset due to using `type` as a reference target then.

For the better or worse, revert to using tpe. Though I acknowledge this
means we need to be careful with trailing underscores because our docs
build is so fragile.

Partly reverts b9eabbabba.

scripts/base/frameworks/config/input.zeek

@@ -30,7 +30,7 @@ type EventFields: record {
 	option_val: string;
 };
 
-event config_line(description: Input::EventDescription, type_: Input::Event, p: EventFields)
+event config_line(description: Input::EventDescription, tpe: Input::Event, p: EventFields)
 	{
 	}