Remove nightlies bucket, the repo no longer exists

[Hamled]

Description

This removes the "nightlies" bucket from buckets.json as the repo associated with it (https://github.com/ScoopInstaller/Nightlies) no longer exists.

Motivation and Context

This was resulting in an error message from the Invoke-WebRequest cmdlet being displayed to when scoop search was used (and possibly other commands).
Relates to #4574

How Has This Been Tested?

I've verified that when this entry is no longer in buckets.json the scoop search command does not produce an error related to requesting that repository.

Issue #4574 should still be fixed separately however, as there are other sources of potential failure by the Invoke-WebRequest cmdlet that should be handled.

[rashil2000]

Already done 48b035d

Wait for a few days for new release

[Hamled]

My bad, I was looking at the master branch instead of develop 😄