Bug on repeatable qualdrop value

[atarix83]

Describe the bug
trying to delete a qualdrop fields with different metadata generates an error

To Reproduce
Steps to reproduce the behavior:

1. start a new submission with a qualdrop value field (e.g a publication has Identifiers field)
2. enter a new identifier
3. save submission
4. click add more to add a new identifier
5. select a different identifier than the one saved before
6. enter the new identifier
7. save the submission
8. click on the Trash icon to delete the last identifier added
9. save the submission an error message should be displayed

Expected behavior
The delete operation should be saved successfully

[atarix83]

@tdonohue it takes 1hour to fix, I can include fix directly in the current #1201

[tdonohue]

@atarix83 : Sounds good. Moving onto the 7.0 board. Feel free to fix in 1201