refactor!: remove deprecated timezone utils

[barredterra]

Depends on #20253, please merge that one first, then rebase this PR.

Docs: https://github.com/frappe/frappe/wiki/Migrating-to-nightly-version-(future-v15)#renamed-timezone-utils

[codecov]

Codecov Report

Merging #20255 (0a6c2cf) into develop (c099b67) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head 0a6c2cf differs from pull request most recent head db92d1c. Consider uploading reports for the commit db92d1c to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #20255      +/-   ##
===========================================
- Coverage    63.90%   63.90%   -0.01%     
===========================================
  Files          757      757              
  Lines        68695    68689       -6     
  Branches      6176     6176              
===========================================
- Hits         43900    43896       -4     
+ Misses       21269    21267       -2     
  Partials      3526     3526              

Flag	Coverage Δ
server	68.91% <ø> (+<0.01%)	⬆️

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