refactor(core): remove unused field (angular#59184)

Removes the `prefetchTriggers` field from the `TDeferBlockDetails` since we weren't reading or writing to it anywhere.

PR Close angular#59184

Author: crisbeto

packages/core/src/defer/instructions.ts

@@ -119,7 +119,6 @@ export function ɵɵdefer(
       loadingPromise: null,
       providers: null,
       hydrateTriggers: null,
-      prefetchTriggers: null,
       flags: flags ?? TDeferDetailsFlags.Default,
     };
     enableTimerScheduling?.(tView, tDetails, placeholderConfigIndex, loadingConfigIndex);

packages/core/src/defer/interfaces.ts

@@ -140,11 +140,6 @@ export interface TDeferBlockDetails {
    */
   hydrateTriggers: Map<DeferBlockTrigger, HydrateTriggerDetails | null> | null;
 
-  /**
-   * List of prefetch triggers for a given block
-   */
-  prefetchTriggers: Set<DeferBlockTrigger> | null;
-
   /**
    * Defer block flags, which should be used for all
    * instances of a given defer block (the flags that should be