Drop unused throw() helper from TemplateParseError

`TemplateParseError` exposed a `throw(): never` method that was never
called anywhere in the codebase, and the sibling base class
`TemplateExpansionError` did not expose the same helper.  The
asymmetry is dead surface area — `throw error` is idiomatic — so
remove the helper rather than mirror it onto the expansion side.

Reported by CodeRabbit in
#758 (2026-05-11).

Assisted-by: Claude Opus 4.7 (1M context)

Author: 2chanhaeng

packages/uri-template/src/template/errors.ts

@@ -55,9 +55,6 @@ export class TemplateParseError extends Error {
     super(`${message} (at position ${position}): ${hint}`);
     this.name = "TemplateParseError";
   }
-  throw(): never {
-    throw this;
-  }
 }
 
 /**