Automatic merge from submit-queue (batch tested with PRs 45508, 44258, 44126, 45441, 45320)

Removed 'default' row from test_owners.csv and Updated update_owners.py

**What this PR does / why we need it**:
Removes the 'default' row from test_owners.csv and the validation/update logic associated with it in update_owners.py.  
The 'default' row is being removed because it results in too many issues being assigned to the default test owners when issues are automatically generated.

**Release note**:

```release-note
NONE
```
/assign