Improve key updating performance.

[ni4]

...and remove some amount of old, not more needed, code.

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.

Project coverage is 83.89%. Comparing base (45e3392) to head (688780a).
Report is 4 commits behind head on main.

Files	Patch %	Lines
src/lib/pgp-key.cpp	94.59%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2256      +/-   ##
==========================================
+ Coverage   83.77%   83.89%   +0.11%     
==========================================
  Files         113      113              
  Lines       23203    23092     -111     
==========================================
- Hits        19439    19373      -66     
+ Misses       3764     3719      -45     

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[ni4]

Merging as there are two approvals. Thanks!