refactor: Remove unused Delete field from client.Document

[islamaliev]

Relevant issue(s)

Resolves #2274

Description

Remove unused Delete method of client.Document

Tasks

• I made sure the code is well commented, particularly hard-to-understand areas.
• I made sure the repository-held documentation is changed accordingly.
• I made sure the pull request title adheres to the conventional commit style (the subset used in the project can be found in tools/configs/chglog/config.yml).
• I made sure to discuss its limitations such as threats to validity, vulnerability to mistake and misuse, robustness to invalidation of assumptions, resource requirements, ...

How has this been tested?

Unit and integration tests.

Specify the platform(s) on which this was tested:

• MacOS

[fredcarle]

LGTM. If we ever need this at some point we can add it back but I currently can't think of a reason do to so.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8a66721) 74.05% compared to head (cdf6772) 74.11%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2275      +/-   ##
===========================================
+ Coverage    74.05%   74.11%   +0.06%     
===========================================
  Files          256      256              
  Lines        25761    25740      -21     
===========================================
  Hits         19075    19075              
+ Misses        5366     5347      -19     
+ Partials      1320     1318       -2     

Flag	Coverage Δ
all-tests	74.11% <ø> (+0.06%)	⬆️

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

Files	Coverage Δ
client/document.go	70.26% <ø> (+2.41%)	⬆️
client/value.go	93.33% <ø> (+5.10%)	⬆️

... and 8 files with indirect coverage changes

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