Stop relying on fugit

[solnic]

It is an overkill to have a (implicit) dependency
on fugit, especially that it doesn't even offer
a public interface to do what we need.

It's older version don't support timezones in cron which I believe is the culprit in #2513.

Even if it's not, I still think it's a good change.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.32%. Comparing base (a4e76ce) to head (33835f3).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2519      +/-   ##
==========================================
- Coverage   69.78%   69.32%   -0.46%     
==========================================
  Files         125      125              
  Lines        4719     4721       +2     
==========================================
- Hits         3293     3273      -20     
- Misses       1426     1448      +22     

Components	Coverage Δ
sentry-ruby	60.00% <ø> (-0.60%)	⬇️
sentry-rails	96.76% <ø> (ø)
sentry-sidekiq	97.08% <100.00%> (-0.02%)	⬇️
sentry-resque	92.85% <ø> (ø)
sentry-delayed_job	95.65% <ø> (ø)
sentry-opentelemetry	99.31% <ø> (ø)

Files with missing lines	Coverage Δ
...-sidekiq/lib/sentry/sidekiq-scheduler/scheduler.rb	96.77% <100.00%> (-0.11%)	⬇️

... and 4 files with indirect coverage changes