feat(DS-475): do not set selected value on combobox when navigating with Tab

Removed the functionality that would set the selected option in combobox when navigating with Tab.

JIRA:

• https://jira.it.helsinki.fi/browse/DS-475

QA:

• https://storybook-qa.it.helsinki.fi/ds-475-combobox-tab-focus/?path=/story/base-components-combobox--default

Testausohjeet:

• Avaa Patterns/Form/Dynamic -tarina, ja kokeile toimiiko kaupunkivalitsin.