fix: remove duplicate declarations introduced by dev merge

Both dev and demo-backup independently added suppressMonthlyAnnualLink
and isHeadOfficeUser() at different points in their respective history,
so the merge's auto-resolve kept both copies instead of deduping,
causing TS2300/TS2393 build failures.

src/app/core/authentication/authentication.service.ts

@@ -384,14 +384,6 @@ export class AuthenticationService {
     return JSON.parse(this.storage.getItem(this.credentialsStorageKey));
   }
 
-  /** Returns true when the logged-in user is at Head Office rather than a branch login. */
-  isHeadOfficeUser(): boolean {
-    const creds = this.getCredentials();
-    if (!creds) return false;
-    if (creds.officeId === 1) return true;
-    return (creds.officeName || '').toLowerCase().includes('head office');
-  }
-
   /** Returns true when the logged-in user has the "Clerk" role. */
   isClerkUser(): boolean {
     const creds = this.getCredentials();