Reworded the DELETE (previous DROP) key function in Architecture chapter

[Andriciuc]

Readded the DELETE key function based on 1257 in Architecture chapter where we also update from DROP to DELETE.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.49%. Comparing base (506606f) to head (b75c1d4).

❌ Your project status has failed because the head coverage (80.49%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@                Coverage Diff                 @@
##           TDE_REL_17_STABLE     #354   +/-   ##
==================================================
  Coverage              80.49%   80.49%           
==================================================
  Files                     22       22           
  Lines                   2604     2604           
  Branches                 398      398           
==================================================
  Hits                    2096     2096           
  Misses                   430      430           
  Partials                  78       78           

Components	Coverage Δ
access	82.95% <ø> (ø)
catalog	87.55% <ø> (ø)
common	91.80% <ø> (ø)
encryption	75.47% <ø> (ø)
keyring	72.00% <ø> (ø)
src	66.74% <ø> (ø)
smgr	97.27% <ø> (ø)
transam	∅ <ø> (∅)

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[dutow]

What's the reason for this PR? https://perconadev.atlassian.net/browse/PG-1257 is not yet implemented. Documentation should be part of the PR implementing it when it's done.

[Andriciuc]

What's the reason for this PR? https://perconadev.atlassian.net/browse/PG-1257 is not yet implemented. Documentation should be part of the PR implementing it when it's done.

This branch will be merged into @artemgavrilov's PR implementation once done. Thank you!