The crash observed in issue #4335 happens because
delete_large_data_entries is passed a deleted name.
Normally we don't get a crash, but a garbage name and we fail to
delete entries from system.large_*.
Adding a test for the fix found another issue that the second patch
is this series fixes.
Tests: unit (dev)
Fixes#4335.
* https://github.com/espindola/scylla guthub/fix-use-after-free-v4:
large_data_handler: Fix a use after destruction
large_data_handler: Make a variable non static
Allow large_data_handler to be stopped twice
Allow table to be stopped twice
Test that large data entries are deleted
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