chore: delete unused functions [RM-41]

[kkunapuli]

Description

chore: delete unused functions RM-41

CheckExperimentExists and CheckTrialExists are not used in the codebase. Rather than bunifying them, we can delete them; they can be added back in if we ever need them

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

Ticket

RM-41

[netlify]

✅ Deploy Preview for determined-ui canceled.

Name	Link
🔨 Latest commit	0d1812f
🔍 Latest deploy log	https://app.netlify.com/sites/determined-ui/deploys/65dcbca6dc03e00008cf6268

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 47.55%. Comparing base (7bb9dbc) to head (0d1812f).
Report is 7 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8888   +/-   ##
=======================================
  Coverage   47.55%   47.55%           
=======================================
  Files        1065     1065           
  Lines      170222   170204   -18     
  Branches     2243     2243           
=======================================
+ Hits        80942    80947    +5     
+ Misses      89122    89099   -23     
  Partials      158      158           

Flag	Coverage Δ
backend	43.37% <ø> (+0.02%)	⬆️
harness	63.82% <ø> (+<0.01%)	⬆️
web	42.53% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
master/internal/db/postgres_experiments.go	54.31% <ø> (+1.32%)	⬆️

... and 3 files with indirect coverage changes

[carolinaecalderon]

Nice catch!