fix(linter/plugins): fix TS types (#14162)

Fix the types. Once I actually used them with `defineRule`, discovered they weren't right.

Author: overlookmotel

apps/oxlint/src-js/plugins/context.ts

@@ -9,7 +9,6 @@ export interface Diagnostic {
   node: {
     start: number;
     end: number;
-    [key: string]: unknown;
   };
   fix?: FixFn;
 }

apps/oxlint/src-js/plugins/types.ts

@@ -11,7 +11,7 @@ export type { Visitor };
 
 // Hook function that runs before traversal.
 // If returns `false`, traversal is skipped for the rule.
-export type BeforeHook = () => boolean | undefined;
+export type BeforeHook = () => boolean | void;
 
 // Hook function that runs after traversal.
 export type AfterHook = () => void;