schemeshard: quick-fix, delete tenant system tablet directly in root hive

[ijon]

Current drop-extsubdomain can leave some system tablets of the tenant hanging out at the root hive and database path and object hanging out at root schemeshard.

Closes #19842.

Changelog entry

Fix problem when deletion of dedicated database could leave some database system tablet not properly cleaned.

Changelog category

• Bugfix

[github-actions]

🟢 2025-07-18 17:09:46 UTC The validation of the Pull Request description is successful.

[github-actions]

⚪ 2025-07-18 17:08:06 UTC Pre-commit check linux-x86_64-relwithdebinfo for c6ac175 has started.
⚪ 2025-07-18 17:08:21 UTC Artifacts will be uploaded here
⚪ 2025-07-18 17:11:48 UTC ya make is running...
🟡 2025-07-18 18:33:10 UTC Some tests failed, follow the links below. Going to retry failed tests...

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
29899	28475	0	7	1389	28

⚪ 2025-07-18 18:35:45 UTC ya make is running... (failed tests rerun, try 2)
🟡 2025-07-18 18:48:41 UTC Some tests failed, follow the links below. Going to retry failed tests...

Test history | Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
290 (only retried tests)	258	0	2	5	25

⚪ 2025-07-18 18:48:50 UTC ya make is running... (failed tests rerun, try 3)
🔴 2025-07-18 19:00:07 UTC Some tests failed, follow the links below.

Test history | Ya make output | Test bloat | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
341 (only retried tests)	322	0	1	0	18

🟢 2025-07-18 19:00:16 UTC Build successful.
🟢 2025-07-18 19:00:37 UTC ydbd size 2.2 GiB changed* by +38.0 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 1d973c6	merge: c6ac175	diff	diff %
ydbd size	2 397 136 136 Bytes	2 397 175 032 Bytes	+38.0 KiB	+0.002%
ydbd stripped size	501 296 200 Bytes	501 303 816 Bytes	+7.4 KiB	+0.002%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}

[github-actions]

⚪ 2025-07-18 17:08:20 UTC Pre-commit check linux-x86_64-release-asan for c6ac175 has started.
⚪ 2025-07-18 17:08:51 UTC Artifacts will be uploaded here
⚪ 2025-07-18 17:12:54 UTC ya make is running...
🟡 2025-07-18 19:08:08 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
14461	14081	0	111	247	22

🟢 2025-07-18 19:09:24 UTC Build successful.
🟢 2025-07-18 19:09:51 UTC ydbd size 3.9 GiB changed* by +98.3 KiB, which is < 100.0 KiB vs main: OK

ydbd size dash	main: 1d973c6	merge: c6ac175	diff	diff %
ydbd size	4 214 442 808 Bytes	4 214 543 424 Bytes	+98.3 KiB	+0.002%
ydbd stripped size	1 460 496 888 Bytes	1 460 534 168 Bytes	+36.4 KiB	+0.003%

^{*please be aware that the difference is based on comparing your commit and the last completed build from the post-commit, check comparation}