chore: simplify fn prune_messages_to_be_saved #2075

Job	Run time
Cargo Shear	21s
Build (ubuntu-latest, dev)	1m 7s
Check	41s
Build (ubuntu-latest, release)	10m 16s
Clippy	1m 11s
Build (windows-latest, dev)	9m 24s
Rustfmt	13s
Build (windows-latest, release)	22m 28s
Build (macos-latest, dev)	1m 6s
Test	2m 25s
Build (macos-latest, release)	7m 51s
Code Coverage	2m 48s
	59m 51s

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