tst_helpengineplugin: remove call to removed method loadBuiltins()


loadBuiltins() does not exist anymore, and does not need any
replacements.

Change-Id: I6706d9e0775e711d0ce0bdc6786631f140f65ef9
Reviewed-by: Olivier De Cannière <olivier.decanniere@qt.io>
commit7df49d768500d25df3f460f1fc0cfd3ec4f1fca7
parentb5d1b06fdae1d5cf929c6765d9fc93f04581a69c
authorSami Shalayel <sami.shalayel@qt.io>
committerSami Shalayel <sami.shalayel@qt.io>
commit timeMon, 12 Oct 2026 11:58:51 +0000