Fix NPE when generated fuzzer class is package-private

[Markoutte]

Description

Fixes #2001

The NPE occurred for every type that is package-private. This fixes the problem by removing excess declaringClass call.

How to test

Automated tests

There's no implementation at the moment but there's a task to do it.

Manual tests

The example from the issued must work.

Self-check list

• I've set the proper labels for my PR (at least, for category and component).
• PR title and description are clear and intelligible.
• I've added enough comments to my code, particularly in hard-to-understand areas.
• The functionality I've repaired, changed or added is covered with automated tests.
• Manual tests have been provided optionally.
• The documentation for the functionality I've been working on is up-to-date.