Cleanup the front end for Utsav 2025 Volunteer Entry

[abhikpai]

1. Change the Utsav Welcome Page Message from MAHE Utsav Coordinators App UTSAV 2024! to MAHE Utsav Coordinators App UTSAV 2025!

2. Hide Slots, Volunteers, Event Standings, Practice Slots, Stats, Certificates from the nav bar

3. Hide "Download" Certificates Button from"
   a) https://manipalutsav.com/volunteers/core
   b) https://manipalutsav.com/volunteers/event