Mainly this PR removes global db::config and feature service that are used by sstables::test_env as dependencies for embedded sstables_manager. Other than that -- drop unused methods, remove nested test_env-s and relax few cases that use two temp dirs at a time for no gain.
Closes#12155
* github.com:scylladb/scylladb:
test, utils: Use only one tempdir
sstable_compaction_test: Dont create nested envs
mutation_reader_test: Remove unused create_sstable() helper
tests, lib: Move globals onto sstables::test_env
tests: Use sstables::test_env.db_config() to access config
features: Mark feature_config_from_db_config const
sstable_3_x_test: Use env method to create sst
sstable_3_x_test: Indentation fix after previous patch
sstable_3_x_test: Use sstable::test_env
test: Add config to sstable::test_env creation
config: Add constexpr value for default murmur ignore bits
a4b77a5691