[BREAKING] - remove is_deleted for Connection model #966

Job	Run time
MSSQL tests / Run MSSQL tests	3m 44s
Oracle tests / Run Oracle tests	4m 7s
MySQL tests / Run MySQL tests	3m 27s
Clickhouse tests / Run Clickhouse tests	3m 48s
HDFS tests / Run HDFS tests	7m 41s
Hive tests / Run Hive tests	4m 15s
S3 tests / Run S3 tests	7m 45s
Scheduler tests / Run Scheduler tests	2m 51s
Unit tests / Run unit tests	3m 9s
Tests done	15s
	41m 2s

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