Remove parallel restore feature

[jzhou77]

This feature is removed and we'll use bulk loading mechanism for restoring a cluster in the future.

Put this in draft mode until new backup is fully qualified.

20250425-051235-jzhou-7392bc7100f7123f compressed=True data_size=35263669 duration=5404578 ended=100000 fail=2 fail_fast=10 max_runs=100000 pass=99998 priority=100 remaining=0 runtime=0:54:19 sanity=False started=100000 stopped=20250425-060654 submitted=20250425-051235 timeout=5400 username=jzhou

2 failures are unrelated:

-f ./tests/fast/KillRegionCycle.toml -s 3267172411 -b on
-f ./tests/rare/BlobRestoreTenantMode.toml -s 3245633057 -b on

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