fixed unupdated config when deleting component

[JamalAlabdullah]

Description

• Updated deleteItem function in FormItemtilte to get the config updated
• updated test

Related Issue(s)

• #12358

Verification

• [ ] Your code builds clean without any errors or warnings
• [ ] Manual testing done (required)
• [ ] Relevant automated test added (if you find this hard, leave it and we'll help out)

Documentation

• [ ] User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)