[BUG] Delete required capability in a contribution throwing error

[sandeep-ps]

Describe the bug
When deleting a capability, if the capability is a "required capability" in a talent, it throws an error.

To Reproduce
Steps to reproduce the behavior:

1. Create a contribution with capability and talent
2. In the talent, select the capability as a required capability
3. Try to delete the capability using "Delete capability" button
4. See error

Expected behavior
Do a validation before deleting the capability.

Additional context
Add any other context about the problem here.

[minump]

Not able to reproduce the error as above. However, the error still persists in another fashion.

Steps to reproduce the behavior:

1. Create a contribution with capability and talent
2. In the talent, select the capability as a required capability
3. Try to delete the capability using "Delete capability" button. The capability will be deleted
4. See the talent details page. Click the link to the required capability.
5. See Error in screenshot
6. The capability id and link persists and arises in a KeyError.
   

The deleted capability is deleted from the DB.

[minump]

This is kept on hold for now.

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