fix: remove deleted events from cron actions

[uds5501]

Fixes fossasia/open-event-frontend#3346

Changes proposed in this pull request:

• Removes deleted events from cron actions like sending email after completion.

Checklist

• I have read the Contribution & Best practices Guide and my PR follows them.
• My branch is up-to-date with the Upstream development branch.
• The unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

• All the functions created/modified in this PR contain relevant docstrings.

[codecov]

Codecov Report

Merging #6295 into development will not change coverage.
The diff coverage is 0%.

@@             Coverage Diff              @@
##           development    #6295   +/-   ##
============================================
  Coverage        65.54%   65.54%           
============================================
  Files              286      286           
  Lines            14589    14589           
============================================
  Hits              9562     9562           
  Misses            5027     5027

Impacted Files	Coverage Δ
app/api/helpers/scheduled_jobs.py	21.42% <0%> (ø)	⬆️

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[uds5501]

@iamareebjamal done