MultiSelectBox renders SelectBox Header when displaySearchBox is false

[markusguenther]

Description

While testing the PR #3536 I tried to enable and disable the search box via the feature list. For the MultiSelectBox the disabled SearchBox was still visible.

Expected behavior

The space of the search field is gone when the search is disabled.

Actual behavior

The bottom space is the empty select box header.

Affected Versions

Neos: 7.3

UI: 7.3