Delete sharded rocks extraneous code (logWriteSize function and its callsites)

[spraza]

As title. This was added in #12583. I observed it while debugging a separate issue. After talking with Gideon, this code was deemed extraneous, therefore deleting it in this PR.

100K should not be needed but running it just in case: 20260112-231338-praza-shardedrocks-debugcod-0089376612d67eb9 compressed=True data_size=34487960 fail_fast=10 max_runs=100000 priority=100 sanity=False submitted=20260112-231338 timeout=5400 username=praza-shardedrocks-debugcode-99ef7aab415b2f161cc0e3444043f492bedb7b1f.

Will make sure 100K is clean before merging.

---

100K results: 20260112-231338-praza-shardedrocks-debugcod-0089376612d67eb9 compressed=True data_size=34487960 duration=4364930 ended=100000 fail_fast=10 max_runs=100000 pass=100000 priority=100 remaining=0 runtime=3:38:59 sanity=False started=100000 stopped=20260113-025237 submitted=20260112-231338 timeout=5400 username=praza-shardedrocks-debugcode-99ef7aab415b2f161cc0e3444043f492bedb7b1f

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[gxglass]

thanks for taking care of it.

[foundationdb-ci]

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[foundationdb-ci]

Result of foundationdb-pr-macos on macOS Ventura 13.x

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[foundationdb-ci]

Result of foundationdb-pr on Linux RHEL 9

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[foundationdb-ci]

Result of foundationdb-pr-clang on Linux RHEL 9

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Result of foundationdb-pr-cluster-tests on Linux RHEL 9

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