How can I remove all alarm times from the clock app?
I think if you have access to Siri you can ask her to delete all your alarms. Simply long press your home button and say "Hey Siri" and then ask her to "delete all your alarms".

If you don't have access to Siri on your device, which you might not, given your vintage of iOS you're out of luck from what I'm finding when searching for this.


How to Delete or Disable All Alarms on Your iPhone
[Tip] Delete all alarms at once in iOS


excerpt


  The stock iOS Clock app is quite functional but it does lack an
  important feature. It doesn’t let you delete all alarms at once in
  iOS, which would be a very convenient option for those who end up
  having a dozen or more alarms that are not relevant anymore.
  
  Normally, you’d need to enter ‘Edit’ mode and hit the delete button
  for each alarm you want to remove. In many cases, avoiding all this
  manual work is what causes all those alarms to pile up in the first
  place.
  
  While the stock Clock app doesn’t have a ‘Delete all’ option, Siri
  provides a solution. Since Apple’s virtual assistant integrates with
  the Clock app, among the many other things it can do, is you can use
  it to delete all alarms at once in iOS.


NOTE: if you have many alarms (>100, approximately), Siri might say "Sorry, there is something wrong. Please try again", as shown in the screenshot below. The issue is due to the fact that the Clock application takes some time to remove all alarms, which exceeds Siri's timeout. Siri will have removed some alarms though: just repeat the voice command  a few more times until Siri confirms all alarms were removed.



References


[Tip] Delete all alarms at once in iOS